For all those others out there who are just as befuddled as I am, this is my problem:
Who is R.A.B.?

I'm assuming Regulus Black (seeing as he was under Voldie and could therefore have suspected about the whole Horc- Horc-.... soul splitting thing.) Plus when I looked up his name, Regulus apparently comes from the Alpha Leo constellation (hence the 'A' middle name). This, so far, is probably the best bet.

Any other takers?