Harry Potter and the Half Blood Prince

Yea, I suppose it would have to be Regalus. One thing JK seems to do is bring back seemingly unimportant characters, and give them a bigger part in the story, so there's a good chance it could be Regalus. Of course, she could simply introduce someone new. Since everyone is expecting it to be Regalus, I wouldn't be surprised if JK does bring in a new character. But JKR has always had the technique to fool and awe the ones who least expect it..... The thing she does is mention things in books that you don't pick up on until you've read what they are used

I've never read any of the books and I don't plan on it. That aside. All these things mentioned, I thought I should point out are attributes of a really good author. She's not the only one who does this. Lots a Stephen Kings(hes just the only one off the top of my head right now) books do. Even his books that don't relate to each other, somehow they do in tiny ways it's crazy. Anyways peace.