I have to say that I have always believed it to be Regulus but NOTHING is set in stone until we hear it from JKR herself. Don't believe every little thing that someone says. JKR doesn't even talk to her husban about this, why would she confide in a stranger? Plus all the people that do know something have been sworn to secret so take this with a grain of salt....but I still believe that it is Regulus anyway!