The sixth of seven books will be released this week.
Any speculations on who the Half-Blood Prince is?
I think it may be Draco Malfoy. He is from a 'pure' family, but JK Rowling does say on her site that "none of these families is really pure - in other words, they simply cross off Muggles and Squibs off the family tree and pretend that they didn't exist." Also, "This subject (pure-bloods not being fully pure) is touched upon in 'Half-Blood Prince.'"
I think it may be a clue from JK Rowling that the Half-Blood Prince is a "pure-blood."
On the other hand, we know little about Nearly Headless Nick except of his execution and that he was some form of royalty. I believe he may be the Half-Blood Prince too, as, he could fit the 'prince' part.
Thoughts on who the Half-Blood Prince is?