It's official. The title of book 6 will be Harry Potter and the Half Blood Prince according to author J.K. Rowling, who officially confirmed the name of book 6 under the News section of her Web site:
Well, the door opened at last and I showed you the title of book six - the genuine title, the title that will appear on the published book, the title I have been using in my head for ages and ages. Unfortunately, however, the door opened on the very same day the 'Pillar of Storgé' hoaxer struck, which left a lot of Harry Potter fans bemused as to whether I was having a joke at their expense by posting another fake title to 'teach hoaxers a lesson', something I certainly wouldn't do, as it would simply frustrate, confuse or annoy the 99.9% of you who aren't hoaxers! I tried to give a clear hint that the title behind the door was the real one by making the 'Toenail' joke as well (see 'Rumours'). But just to clear up matters once and for all…
Information you take directly from this site will be truthful and accurate (I might occasionally joke, but as time goes on, you'll learn to tell when I'm joking). Do not trust anybody else claiming to have found information on this site that you cannot access, however seemingly convincing the images they provide to support their story.
I never post information on the site that I do not want fans to read immediately. In other words, anybody claiming to have 'discovered' a message that wasn't due for release yet is lying. There was never anything meaningful behind the door until the 'Do Not Disturb' sign came off!
Read the rest of what she has to say, including who this "Half Blood Prince" might be (or definitely isn't).