I like to think that Regulus left some kind of letter for Sirius, tucked away in his drawer, somewhere. I always have been a sucker for sibling relationships, and I like to think that Regulus regretted Sirius' leaving, and that Sirius always had a soft spot for his brother. I have also randomly made it my headcanon that after Sirius ran away, Regulus, out of hurt, stopped calling Sirius his brother, so the letter is supposed to be somewhat of an apology for that as well as a goodbye.
This was written randomly in less than ten minutes, apologies for any spelling errors.
Sirius,
If you are reading this now, it means I was not able to tell you in person and that I am likely gone from this world. I go now to what you Gryffindors would valiantly name your Last Battle, one which I will be facing alone and one which will be ending with my death. I can only apologise, Sirius, and say that you were right – I should have listened to you when I had the chance.
I cannot say much within the contents of this letter, but I shall tell you what I can. I have discovered information referring to Voldemort himself, and I go to destroy it, although I know what to expect, there will be no return from it. I have discovered the existence of vile objects – although I have only identified one, myself – which must be destroyed. I have no certain idea of the number of objects but my best guess would be seven – for Voldemort is insistently obsessed with such a number. I have my suspicions of what the others may be, but dare not write it down, instead, Kreacher will tell you, and only you, of the thoughts I left him by word of mouth, for I have ordered it so.
I leave the task of their destruction to you, for despite the fact that this one act will take my life, I know you will be able to discover better ways in undertaking this job, whilst staying intact. You always did have more lives than a cat, you were always resilient, whilst I cannot say the same for myself.
There is so much more I wish to say to you, but a letter would not hold it all, no matter how much quill, ink and parchment I use. All I can do now is say that I am sorry. I am sorry for ignoring you, for causing you pain, whether it be directly or indirectly. I am sorry for the distance that grew between us, and I like to think that if we could have met again, we could have mended our relationship, bridged the gap. You were always so forgiving of me, brother, and I wish that I deserved it. I know that in my ignorance I grew more cold towards you, angrier, and I am sorry for it. I hope that in my last act of defiance you would be proud of me, once more.
Your little brother,
Reg
