I think you are all forgetting one huge fact. The only people who call him "The Dark Lord" are death eaters, or former death eaters like Snape. This points right to Sirius' Brother Regulus because he was a death eater. Don't make it harder than it sounds because if it's not him there is no way you guys are going to figure it out. So just stick with him until the next book comes out.
Has anyone seen this?
http://www.hp-lexicon.org/wizards/regulus.html
I don't know who the "well-placed source" on 28 August, 2005 was, but usually Lexicon is pretty reliable. But as they won't say who this source is, I'm not sure what to think 😕
Wow. RAB confirmed.(well almost)
its Regulas Arcturus Black.
http://www.hp-lexicon.org/wizards/regulus.html
Now they didnt say how it was confirmed, but this is like one of the biggiest HP sites and i dont know why they would keep saying its definatley him.
I know there is a thread about this, but i felt it deserved a new one. Sorry though.