I can't believe none of you haven't realized what it could be. Granted, I might be dead wrong, but here goes. The rumours said that the book has some sort of tie-in with the second book, right? And the official comment said that it is neither Harry nor Voldemort, right? Well, what character were we introduced to in the second book who was half blood, that wasn't Harry of Voldemort? I'll tell you who. Tom Marvolo Riddle. You'll remember Harry was confused about what Dobby said about Voldemort not being involved in the chamber of secrets, to which Dobby replied, " Was giving you a clue. The Dark Lord, before he changed his name, could be named freely, you see?". If that aint proof that it's Tom riddle, then I sure am stumped. And it ties right in with the word of J.K.R. She said nothing about Tom:)