The sixth Harry Potter book is to be called Harry Potter and the Half Blood Prince.

J K Rowling revealed the new name on her official website - but by way of a complicated set of clues that only hardened fans would fathom.

After the latest in a long line of hoax titles came out on the same day she revealed the real title, she said ''super-bright fans'' would know her title was genuine because it was once considered as an alternative title for Harry Potter and the Chamber of Secrets.

Referring to the hoax, which claimed the book had had a last minute change of name to ''The Pillar of Storge'' because she had been ''found out'', Rowling says: "I nearly fell off my chair giggling when I read about this."

However as a bonus to appease those she feels may have been fooled by all the different stories, she reveals that the half blood prince referred to in the title is neither Harry himself nor Voldemort.

She also promises to reveal more information in stages as the still unfinished book is completed.

And she hints that anyone wanting to know how the series will end may need to re-read the Chamber of Secrets, the second book in the series.

"Certain crucial pieces of information in book six were originally planned for ''Chamber of Secrets'', but very early on (first draft of Chamber) I realised that this information''s proper home was book six," she says.

"I have said before now that ''Chamber'' holds some very important clues to the ultimate end of the series."