AN: A little drabble I thought of and wrote this morning... because I'm still not over the fact Sirius died without knowing the truth behind Regulus' death. As I've mentioned in the summary, this is an AU in which Sirius didn't die in the fifth book and is set at some point during the Deathly Hallows.

I hope you enjoy it! Please leave a review to tell me what you thought of it!

To the Dark Lord,

I know I will be dead long before you read this

but I want you to know that it was I who discovered your secret.

I have stolen the real horcrux and intend to destroy it as soon as I can.

I face death in the hope that when you meet your match,

you will be mortal once more.

R.A.B.

Sirius traced the initials with his fingers, a faraway look on his face.

The image of a boy flashed through his brain, a boy not much older than his own godson. A boy who was pale and dark-haired, his eyes wide and afraid as he spoke words Sirius could no longer recall. It had been raining that day.

"Well, Sirius?" Harry prompted, giving his godfather an expectant look. "Do you have any idea who it could be?"

"Just one." Sirius admitted. He wet his lips. "It's not very likely though."

"That's alright- any lead at all would be helpful."

"Yeah," Ron agreed, "we've been cracking our heads about it all summer."

Sirius looked at the three teenagers standing before him- just children, really- and wondered what on Earth the old headmaster had been thinking when he assigned them this task. They were kids, and now they were not only caught up in a war but also in something much darker than anybody their age (or indeed anybody at all) should know of.

"It might be a coincidence, so I don't know this for sure but... those initials correspond to somebody I used to know."

Harry, Ron and Hermione exchanged excited looks, and despite himself, Sirius couldn't help but smile a bit. Out of nowhere came the urge to reach out and ruffle their hair- to tell them not to work too hard... but that's not a luxury they had amidst the war.

"Who is it?" Harry asked eagerly, at the same time as Hermione said: "Do you know where we can find them?"

"He's dead... died over eighteen years ago."

There had been a night, over eighteen years ago, when a dark-haired boy had stood at his doorstep. He had been soaked in rainwater from head to toe, his frame trembling from the heavy cold, and he had looked nothing less than miserable. The dark circles under his eyes spoke of many sleepless nights, but all Sirius had seen at the time was a Death Eater.

Get the hell off my porch, Regulus.

And he did.

It was the last time Sirius ever saw the boy again.

"My brother's middle name was Arcturus, after my father's father. Regulus Arcturus Black. R.A.B. ... He always used to sign his letters with those stupid initials, the pompous prat." There was no real malice in his words, just a feeling of melancholy.

"Regulus..." Harry gave him a puzzled look, "but, Sirius... didn't you say your brother was a Death Eater?"

"He was. Joined as soon as he was old enough to."

"But why would a Death Eater-"

"No, no- it makes sense." Hermione spoke up. "He would be close enough to Voldemort to figure it out... and maybe he became disillusioned. Which is why he wanted to bring him down."

All three heads turned to Sirius, as if awaiting confirmation. He thought he knew what they were thinking: Sirius was his brother. Ergo, he should know if their theory was plausible. Sirius wished that he did. He really, really did.

"Even before he died, Regulus and I hadn't had a civil conversation since... Hogwarts. Fourth year, maybe. I'm as much in the dark as you guys."

"Oh..."

There was a moment of silence during which each of them was lost in their own thoughts.

For the first time in years, Sirius thought- really thought- about the boy that was Regulus Black.

Could he have done it? Could he have turned against Voldemort and everything he had previously stood for? Could he have given his life to bring his master down? Sirius had always believed him to be a coward and a fool but could he even still be sure of that?

And if that were the case, why hadn't the idiot tried to ask for help?! The Order could have used the information, and he wouldn't have had to die.

It was a guilty little voice in the back of his mind that told him that Regulus did try to ask for help once. Only that Sirius threatened to hand him over to the dementors when he did.

Now, the memory made him shiver... it had been a horrible thing to say.

He thought of his little brother being thrown in Azkaban- the little brother who was slighter and younger than him and very prone to colds- and it made him want to hurl.

"There was a locket!"

"What?"

"In the cabinet in the drawing room. Nobody could open it. And we... we..."

Oh.

…

Kreacher had taken off to find Mundungus a couple of hours ago.

As Sirius sat in the kitchen, a cup of steaming hot coffee in his hands, Kreacher's tale just kept repeating itself inside his mind.

Regulus had turned against Voldemort, and that was the reason why he was dead. Not because he had gotten cold feet, or because he had tried to run away.

No, he had gone to that cave fully aware that he would die. And he had done it to bring down Voldemort.

He could see it clearly in his mind's eye: a dark-haired, pale boy, no older than eighteen years of age standing by his house-elf as they crossed a dark lake filled with inferi. Of course Regulus wouldn't let Kreacher drink the potion- Sirius had hated the damn thing, but Kreacher had practically raised Regulus. His brother might have been many things, but cruel had never been one of them.

"Are you alright, Sirius?" It was Hermione's soft voice that broke him out of his thoughts. Sirius looked up and found the girl in question standing in the doorway, her arms casually crossed over her chest. He wasn't quite sure for how long she'd been standing there.

"I'm fine, don't worry about it."

"Alright. I just wanted to say... I'm sorry about your brother..."

"Yeah..." Sirius sighed, taking a sip from his coffee. "Yeah, me too..."

He wished that he had something stronger to drink than coffee, in fact, a bottle of firewhiskey to knock him out for a couple of hours sounded like a great idea right about now.

Hermione walked over to the table and sat down next to him. With a flick of her wand, a cup zoomed out of the cupboard and landed in front of her. Sirius filled it for her.

"Thanks."

"No problem."

Neither of them said anything for a couple more moments, just listening to the sounds of Harry pacing back and forth inside the drawing room. Sirius wasn't sure where Ron was, but his room sounded like a pretty safe bet.

Automatically, his mind veered back to Kreacher's words.

To the way his brother drank that terrible potion, and the way he told the old house elf to leave him behind and never tell anybody about what had happened. It was a sacrifice.

A necessary evil, in order to keep those he cared about safe. After all, family had always been important to Regulus.

It made the hard, unforgiving truth, the fact that he had turned Regulus away that night, much more difficult to stomach. Merlin, he might as well have killed his brother himself!

"What was he like?" Hermione suddenly questioned. "Regulus?"

"I'm not even sure if I know anymore..."

"Well... what do you know about him?"

Sirius looked up and turned his gaze towards Hermione. She was watching him expectantly, looking like she was genuinely interested in finding out all that he knew about a boy who had died many many years ago. Despite himself, Sirius smiled.

"He always used to sit where you're sitting." He slowly said, "My seat was this one right next to it. When we were about five or six we carved our names onto our chairs- needless to say of course, Mother wasn't impressed."

Then again, Sirius thought, Walburga Black was hardly ever impressed.

"He was soft-spoken... kind of bookish... yeah, he used to read a lot. He was proud to be a Black though." Sirius remembered something and rolled his eyes in exasperation. "He would always introduce himself the formal way. You know, the whole: Second Heir to the Noble and Most Ancient House of Black, thing. James thought it was funny. They never really got along, the two of them."

"There's a picture of the Slytherin quidditch team in his room... he played, right?" Hermione inquired.

"Oh yes. He was the seeker, joined at the beginning of his third year, I think. He was really good... loved flying."

"Like Harry?"

"... Yeah, kind of like Harry. Actually," Sirius chuckled, "we always used to play quidditch together, when we were little. Outside, or in the living room when it was raining."

"In the living room?"

"Not my brightest idea, admittedly. But yes, he was definitely good at quidditch. One of Slughor's favourites and a prefect."

"He doesn't sound that bad..."

Sirius sighed, running a hand through his hair.

It was a truth he'd been running from for years- the plain truth that it wasn't Regulus who had pushed him away because of his pureblood believes and prejudiced thoughts... but that he had been the one to push Regulus away. Because he wanted to go against their parents. Because he was a Gryffindor. Because he had James.

"You're right. He wasn't..."

And just like that, he was admitting to it. To his mistakes.

Because yes, Regulus had been proud to be a Slytherin, a pureblood and a Black. He had hated James Potter the moment he had met him, and had done everything in his power to push him away from Sirius during his first year at Hogwarts. And later he had become a Death Eater. He had probably killed people before he decided to try and bring down Voldemort.

Regulus wasn't a saint, but neither was he.

He had pushed Regulus away, and not the other way around. Because James was cooler and better and Gryffindor. Because at the time he had thought everything Slytherin was bad. Because Regulus was his annoying little brother. He had been a jerk to many students, his little brother included, and who could forget the night Regulus had come to him for help and Sirius had told him to get off his porch before he called the dementors on him?

Regulus hadn't been that bad.

He hadn't deserved to die.

He had been but a child, caught up in a world he didn't understand and couldn't escape.

"Blacks are often named after the stars..." Sirius finally said, causing Hermione to look at him again. He had been quiet for a while. "Regulus... Regulus is the brightest star of the Leo constellation."

"That's oddly ironic."

"I know."