JK Rowling has posted the following on her site about the connection between book 6 and book 2:

"I have been engulfed by an avalanche of questions on the subject of 'Prince' having once been a title of 'Chamber'. I am therefore attempting to answer most of them under this heading, which I think just about covers all the answerable variations (the unanswerable ones include questions such as 'who's the Half-Blood Prince?' 'what happens in the Half-Blood Prince?' and 'what does Half-Blood Prince mean?')

The plot of 'Prince' bears no resemblance whatsoever to the plot of 'Chamber', nor is it an off-cut of 'Chamber'. The story of 'Prince' takes off where 'Phoenix' ended and does not hark back to four years previously. True, mention is made to events that happened in 'Chamber,' but of course, mention is also made of events that happened in 'Stone', 'Azkaban', 'Goblet' and 'Phoenix'.

'The Half-Blood Prince' might be described as a strand of the overall plot. That strand could be used in a whole variety of ways and back in 1997 I considered weaving it into the story of 'Chamber'. It really didn't fit there, though; it was not part of the story of the basilisk and Riddle's diary, and before long I accepted that it would be better to do it justice in book six. I clung to the title for a while, even though all trace of the 'Prince' storyline had disappeared, because I liked it so much (yes, I really like this title!). I re-christened book two 'Chamber of Secrets' when I started the second draft.

The link I mentioned between books two and six does not, in fact, relate to the 'Half-Blood Prince' (because there is no trace left of the HBP storyline in 'Chamber'.) Rather, it relates to a discovery Harry made in 'Chamber' that foreshadows something that he finds out in 'Prince'."


"Rather, it relates to a discovery Harry made in 'Chamber' that foreshadows something that he finds out in 'Prince'" Hmm... what is she hinting at? Does it have something to do ith Draco?