Who is R.A.B?

[Kahlessa]

Who is the R.A.B who left the note inside the fake locket horcrux? Most people seem to think that R.A.B. is Sirius’ brother Regulus Black, with his middle initial A standing for Alphard. Sirius Black mentioned that he had an uncle named Alphard.

J. K. Rowling acknowledged that Regulus would be a "fine guess" for R.A.B.'s identity.

And what is Voldemort’s secret that he refers to in the note? Is it the use of the horcruxes, or is it something else? Any theories?

[Lukaran]

Whether it was Regulus Black or not, I wonder how RAB managed to get the locket? Remember what happened with Dumbledore and Harry. Dumbledore said one person could not have done it alone. So if Regelus did switch the locket, who went with him?

[Kahlessa]

lukaran9 said:

Whether it was Regulus Black or not, I wonder how RAB managed to get the locket? Remember what happened with Dumbledore and Harry. Dumbledore said one person could not have done it alone. So if Regelus did switch the locket, who went with him?

Assuming that the locket was switched after it was placed in the cave. The locket could have been switched before all the magical barriers were in place. I read a very interesting theory about this that I'll explain more of later.

[Kahlessa]

There's a very interesting theory about Regelus Black and the Black family:

Harry Potter and the Curse of the Black Family Tree
(sorry, no working link available)
By Wendy B. Harte
From the book Who Killed Albus Dumbledore? Edited by John Granger, Zossima Press, 2006, ISBN 0972322116

Here's something that helps understand the theory:

"The Noble and Most Ancient House of BLACK", a hand-drawn tree that Rowling donated to Book Aid International in January of 2006 and auctioned February 22, 2006:
www.hp-lexicon.org/wizards/blackfamilytree.html

I guess we'll know soon if the theory is correct, but it is fascinating in any case!