Another candidate for RAB

[eggplant107]

No: HPFGUIDX 150985

Correct me if I'm wrong but I thought the identity of RAB was pretty
much settled from what we know about the translations of the books. In
Finnish the Black family name is translated as Musta and the initials
become RAM, in Dutch Black is Zwarts and we get RAZ, in Norweigen
Black is Svarrt and the initials are translated as RAS. 

So RAB must be a member of the Black family with a first name that
starts with an R, I can't think of anybody who fits that bill except
Regulus, besides I can't imagine why JKR would introduce us to a
character like Regulus unless she had need of him in a later book. As
for his middle name I would guess Arcturus or Aldebaran or Altair or
Antares. 

Eggplant