Author's Note: This is entirely ash-castle's fault. Okay, so if Harry was born in July of 1980, that means Lily got pregnant sometime around October of 1979. We don't know exactly when Regulus died, but we know it was sometime in 1979, so if you squint a bit the dates could work.

Thanks, Worthfull1

P.S. I own nothing, anything recognizable belongs to the lovely Ms. Rowling.

A Relative Revelation

Chapter 1: Whose Kid Is It, Anyway?

July, 1995

12 Grimmauld Place

"Pads, Molly's got lunch on the table," Remus said, leaning against the doorway to Regulus' old bedroom.

Sirius didn't answer at first. He was staring at the letter in his hands, unable to believe the words on the parchment. Having finally bitten the bullet and started cleaning out his late brother's bedroom, he'd come across a small box stuffed full of letters. Expecting them to be from Regulus' Slytherin friends, Sirius had not given them much thought until he tossed the box on the bed and one envelope fell out, displaying a very familiar handwriting.

"Sirius? You okay, mate?" Remus asked when the animagus gave no indication of having heard him.

Sirius blinked, as though coming out of a stupor, and turned slowly towards Remus. "You - you've got to - to read these," he stammered quietly, sitting on the bed. The hand holding the letter began shaking.

Remus frowned, but walked up to Sirius and picked up one of the letters scattered across the bed. "What is it?"

"I - I'm not sure."

Opening the letter he held, dated September of 1979, Remus' eyebrows shot up at the first line. 'My Darling Lily-love,' it began. The letter was signed by Regulus, but that didn't make any sense. As far as Remus was aware, Lily had barely known Regulus socially, much less intimately, and 'Darling Lily-love' was most certainly an intimate salutation. He read on.

'I know you hate it when I call you that, but perhaps you'll forgive me when I tell you I only do it so I can see you flush. That angry blush that travels from your pretty cheeks down your long, lovely throat and on towards those perfect breasts. I'm imagining it now…'

"What the - ?" He looked at Sirius. "What the hell is this?"

Sirius nodded, his face troubled. "I know," he said. "They're all like that." He held up the parchment in his hand. "This one's even worse. It's from her, and… and…" He shook his head. "I can't believe what I'm reading, Remus."

"You're sure this is Regulus' writing?" Remus asked. "Dead sure? Without a doubt?"

Sirius took a deep breath. "I'm positive," he said, his voice breaking. "That's… that's not all, though." Remus paused, midway through running a hand through his hair. Sirius held out his letter. "This one says… it says H-Harry may not be James'."

"What?!"

Remus snatched the parchment out of Sirius' hand. It was Lily's handwriting, so familiar it hurt just to see it, calling Regulus Reggie. Just to be sure, Remus brought the letter to his nose and inhaled. Even after fifteen years, Lily's scent still clung to the parchment.

'You asked me last night whose child I'm carrying, and you're right - I can't answer you. I don't know. And I don't want to. It doesn't matter. I will never leave James. Why should I? I can't be a part of what you're doing, and you can't protect me. At least I know the people James associates with aren't trying to kill me. I never intended to get pregnant so soon, but now that I am, the safety of my baby comes first. Above myself, and above you.

I did love you, Reggie. I still do, but if you think I don't love James, you couldn't be more wrong. My love for him is as deep as my love for you was desperate.

Merlin, how did I ever get myself in this mess?

It doesn't matter now. It's over. Please forget about me and move on with your life. I am a Potter, I will remain a Potter, and my child will be a Potter. I'm sending back the letters you've written me. As much as it hurts me to do so, it would hurt me more if James were to find them, not to mention how much it would hurt him, but I don't have the heart to destroy them.

Goodbye for the last time,

Lily

"Fucking hell," Remus muttered, sitting on the bed. He suddenly felt weak in the knees. Would the universe-shattering revelations ever end?

Sirius stood and began to pace. "How could she?" he hissed, shock giving way to anger. "How could she cheat on James? With Reg? Of all people!"

While Sirius paced, muttering angrily and running frustrated hands through his hair, Remus went through the other letters. Apparently, Regulus hadn't had the heart to destroy them, either, and each piece of parchment added another layer to a story Remus had thought he knew. Hell, he'd been there for it.

But, then again, he'd been there for Sirius and Peter's story as well.

"Sirius," he said, interrupting the other man's unpleasant rumblings. "You realize what this means, don't you?"

"That Lily was a lying, cheating slut?!"

Remus scowled, but wasn't surprised. When Sirius was angry, he lashed out. He always came 'round eventually, but the first instinct when hurt was to hurt back.

"You need to read these," Remus said. "All of them. Then you won't be so angry with her."

"I doubt that," Sirius growled. "This was the woman I loved like a sister, James' wife, someone I would have gladly died for, and now I find out she was fucking Death Eaters?!"

"A Death Eater, Sirius," Remus corrected. "And one who happened to be your brother. Are you telling me you wouldn't gladly have died for the woman who gave birth to your nephew?"

Sirius stopped dead in his tracks as though that hadn't occurred to him yet.

"If Harry is Regulus' son - and these letters suggest there's at least a fifty-fifty chance he is - then that means he is your nephew. Flesh and blood. That changes things."

"It does not!" Sirius said, affronted. "I still love him! Maybe more, if that's even possible!"

Remus shook his head. "I don't mean that, Sirius. I mean it changes things legally. You've been bitching and moaning forever about how much hold Dumbledore has on Harry even though you're his godfather. Well, being his uncle would change things. I'll have to look into it, I'm not well-versed on wizarding family law, but I can't help but think an actual blood tie - especially one to a family as old as the Blacks - would throw the quaffle to your side of the pitch."

Sirius stood there, breathing hard, while that sunk in. "I don't want to tell him yet."

"Harry?"

"Dumbledore," Sirius said. "Harry's coming here soon, right? That's what the old man keeps saying? I can be good until he gets here, then we'll talk to Harry first and do a paternity test charm."

"Without Dumbledore?"

Sirius nodded. "Abso-fucking-lutely without Dumbledore," he snarled. "He keeps Harry in the dark about enough shit. If Harry is, in fact, my nephew, then he has the right to know, and he and I have the right to make our own decisions about things. Once I - once we - know what's going on, then we'll tell Dumbledore."

August, 1995

12 Grimmauld Place

"Harry, you got some time after supper?" Sirius asked as the residents of the house dug into another one of Molly's feasts. "Got some things I want to talk to you about."

Harry nodded, a forkful of mashed potatoes halfway to his mouth. "Sure, Sirius. What kind of things?"

Sirius winked conspiratorially. "Family business," he said, knowing that would whet the boy's appetite. Sure enough, Harry smiled - a rare occurrence what with his trial for underage use of magic coming up in just a few days.

When the meal was over, Sirius guided Harry out of the kitchen, bestowing an innocent smile on a disapproving Molly, and led his godson-maybe-nephew into the formal dining room. He and Remus had cleaned a corner of the room earlier so they could have this conversation away from prying eyes and ears. Remus followed them in and erected wards to ensure privacy. Harry watched, frowning.

"This is a bit of a delicate conversation, Harry," Sirius explained. "I know you kids have been trying to listen in on Order meetings and I won't put it past you lot to have succeeded."

Harry looked down, embarrassed. "Sorry."

"Don't be ridiculous," Sirius scoffed. "It's only natural to try and get in somewhere you've been told to stay out of. James and I did it all the time."

Harry's face lit up at the mention of James, and Sirius tried once again to find the truth in the boy's features. He'd been watching Harry since the Order brought him to the house, but it was so hard to see one man or the other in Harry. Both James and Regulus had been slightly shorter than average with thick, jet-black hair. Harry's glasses made him resemble James, but the few times Sirius had seen him without them made it even harder to tell who his father really was.

"Take a seat, Harry," Sirius said, sitting down himself and pulling out the magically shrunken box of letters and a book from his pocket and enlarging them to their proper size. He'd been carrying the letters around on his person at all times since he'd found them, not wanting them to fall into Molly's hands during her cleaning.

"101 Personal Charms?" Harry asked, reading the cover of the book. "What's this for?"

"We'll get to that in a second," Remus said, taking the third chair.

"Harry," Sirius began, taking a deep breath and holding the box of letters in his hand. "First things first. I found this box recently while cleaning out my brother's old room. It's a box of letters. Specifically, love letters. Some are from your mother."

Harry frowned. "Why would love letters from my Mum be in your brother's room?"

Sirius swallowed. "Because… because they were written to my brother," he said, and Harry's eyes widened. "The other letters in here are addressed to her, written by him. It appears that Lily and Regulus were… were lovers."

"What?!" Harry looked from Sirius to Remus and back again as though waiting for one of them to tell him they were joking. "You mean - she had an affair? While married to Dad?" He looked horrified.

"I'm afraid it goes a bit deeper than that, Harry," Remus said. "A lot deeper, actually. From what I read in these letters, Lily and Regulus were together for some time before she even started dating James."

"In school?"

"That's right."

"And you didn't know?" Harry asked, incredulous. "None of you knew?"

Sirius shook his head. "No, Harry. None of us knew."

"You have to understand Harry," Remus said, "Lily and Regulus going out together publicly would have been much the same as Hermione going out with the Malfoy boy. Can you imagine the uproar that would cause? You've met Sirius' mother's portrait, you know how she felt about blood status."

"Wait a minute," Harry said. "Are you saying that my Mum dated my Dad and your brother at the same time?" he asked Sirius.

"No, I don't believe so, Harry," Sirius said. "From what Remus and I can piece together, once your mother started dating James, she broke it off with Reg, and they didn't reconnect until after Reg graduated and your mother married James."

"So, what? She married Dad and then went back to your brother?!"

Sirius shared a look with Remus. Harry's temper was about to get the better of him and neither man could blame him. It was hard enough for them, as grown men, to make sense of what they'd recently discovered; they couldn't expect a teenage boy with no relationship experience to understand.

"Harry, listen to me, please," Sirius entreated. "I know how it sounds. Believe me, I didn't take it well either when I found these, but your mother states quite clearly several times in these letters that she loved James very much - "

"Yeah, just not enough to not cheat on him!"

"Harry," Remus broke in, "relationships can be terribly complicated, even between the best of people, and it's wrong to judge from the outside. We realize this is a lot to take in, and you're going to need some time to digest it, but there are other things we need to talk about tonight as well."

"Other things? What do you mean - oh," Harry said, realization dawning. "No… Sirius?" He looked at his godfather.

Sirius met his eyes. "It appears Lily broke off her affair with Reg shortly after finding out she was pregnant. In her last letter, she says that she doesn't know who the father is." Harry began shaking his head. "Harry, we need to know."

Green eyes flicked to the book on the table. "Is that what the book is for? Is there a charm in there that can tell us?" he asked, watching Remus open the book to a marked page.

"Yes."

"Well, do it!" Harry exclaimed. "Let's find out!"

Remus pulled out his wand. "Alright, Harry, if you would stand, please." He'd been practicing the paternity charm on Sirius all week.

Harry stood, looking slightly wary. "What's going to happen?"

Sirius answered. "You'll feel a slight tingle, and your aura will glow. Your magical signature will hover in front of your chest, while your parent's signatures will hover above that."

"And… and you'll know?"

Sirius nodded. "Yes, Harry. We'll know. Remus and I know James' signature like the back of our hands, and I know Reg's just as well."

Harry took a deep breath, relaxed his arms by his sides, and nodded. "Okay."

"Are you ready, Harry?" Remus asked.

"Yeah."

"Parentalis genius revelio."

Harry shivered as the spell washed over him, and he closed his eyes, not sure he wanted to know the results. "Well?" he asked nervously.

"Legally, you're a Potter," Sirius said. "Magically… you're an Evans-Black."

Harry opened his eyes and stared at the hovering symbols in front of him. Remus cancelled the spell and Harry sat back down, slumping forward and dropping his head into his hands. He was quiet for a long while.

"Is there anything else?" he asked finally, his voice heavy. "Is there anything else being kept from me?"

"We didn't keep this from you, Harry," Remus said. "We only just found out ourselves."

"Please believe me, Harry, I wouldn't have kept this from you," Sirius said. "There are still a couple of things about your situation with Voldemort that you haven't been told yet, but that was Dumbledore's call. Dumbledore doesn't know about this yet."

Harry raised his head and looked at Sirius. "You haven't told him?"

"No. You deserved to know first."

"Thank you."

"You're welcome." Sirius paused. "About these letters… I think you should read them. When you're ready. They will help you understand a bit better, I think, but I should warn you that they are love letters. They do get a bit… heated at times."

"Heated?"

Sirius nodded. "There are a few that get a bit… explicit. Sexually." Harry leaned back a bit in his chair, looking nauseous. "I'll just hang on to them until you're ready, how about that?"

Harry nodded. "Does this… change anything?" he asked.

"You mean legally?" Remus clarified. Harry nodded. "I'm looking into that right now. I've got some books in my room I'm trying to make sense of."

"We can ask Hermione to help," Harry suggested. "She's brilliant at research."

"Are you willing to trust her with this?" Sirius asked. "Remus and I think it'd be best to have our ducks in a row before speaking to Dumbledore. Would Hermione be willing to keep it to herself for now?"

Harry nodded firmly. "She will if I ask her to."

"Hermione," Remus said quietly so as to not be overheard when he entered the sitting room with Sirius and Harry. It wasn't difficult with Ginny and Ron bickering like usual. "Do you think you could sneak over to Ron and Harry's room tonight after everyone's asleep? We need some help with a bit of research."

Hermione looked a bit confused, but she nodded anyway. "Okay."

"Thanks," Remus said. "And if you could keep it quiet…?"

"Um, sure."

Later that night, after everyone had gone to bed, Remus gathered his books and headed to Harry and Ron's bedroom. He knocked lightly and Hermione let him in. Sirius was already there, sitting next to Harry on the boy's bed while Ron sat on his own. Ron and Hermione both looked a bit wary, but Hermione also looked concerned, and Remus thanked the powers that be that Harry had a friend like her.

He put up the privacy wards and looked at Sirius. "What have I missed?"

"Nothing. We haven't started yet."

Remus nodded. "Hermione, Ron - a situation has come up and we'd be grateful for your assistance."

"A situation with Harry?" Ron asked, looking at his friend.

"Yes."

Hermione looked at Harry as well. "Is that why you were acting weird after talking to Sirius tonight?" Harry nodded. "What's happened? Is it about your nightmares?"

"No, Hermione, it's nothing to do with Voldemort," Sirius said.

"Blimey, mate," Ron said, shaking his head. "You sure know how to attract trouble, don't you?" he asked, amused. "So, what's the problem?"

Harry opened and closed his mouth several times but nothing came out.

"Harry, it can't be that bad," Hermione said gently.

Sirius watched his nephew flush and decided to step in. "Would you rather I told them?" he asked. Harry relaxed and nodded. Sirius gave the boy's shoulder a squeeze. "Okay. We found out this evening that James is not Harry's biological father."

Hermione squeaked and her hand flew to her mouth. Ron frowned. "But… but they were married, right?"

"Lily and James? Yes."

"So, do we know who Harry's father is?" Hermione asked, looking from Sirius to Remus.

Remus sighed. "Harry's biological father is Sirius' brother, Regulus." Hermione's head whipped around to stare at Sirius again.

"Hey, don't look at me, kitten! I didn't do it!"

"Sirius!" Remus admonished.

"But he was a Death Eater!" Ron exclaimed, red-faced. "Didn't you tell us he was a Death Eater?"

Stepping in to diffuse teenage tempers, Remus gave Hermione and Ron a quick run-down of the situation, including not wanting to involve Dumbledore just yet.

"But surely Professor Dumbledore would know all about familial law," Hermione argued. "I mean, he is the Chief Warlock, isn't he?"

"No, he was ousted recently," Sirius said, "but even if he was, I happen to be Harry's godfather and uncle. Both of those titles outrank Dumbledore, even though I am still a fugitive, and I think Dumbledore has made enough decisions about Harry."

Hermione still looked unconvinced.

"We're not talking about going against Dumbledore, Hermione. This isn't a mutiny," Remus interjected. "We just think it would be in Harry's best interest for Sirius - and, by extension, Harry - to have a bit more leverage. This an exercise in education. The more we know about where Harry stands legally, the better. Especially with his trial in a few days. We don't want to be blindsided by anything."

Finally Hermione nodded. That made sense to her. Remus handed her a book while Ron fished out some parchment and a quill and ink, and Harry let out a small sigh. Sirius heard it and wrapped an arm around the boy's shoulders.

"Everything will be alright, Harry," he said quietly. "One way or another. You'll see."