In an interview broadcast on BBC One on Friday, the author said that she knows what is going to happen to the series' major characters - including some untimely deaths.
In the programme she allows the cameras to see the final chapter and says: "This is it, and I'm not opening it for obvious reasons.
"This really wrap everything, it's the epilogue and I basically say what happens to everyone after they leave school, those who survive - because there are deaths, more deaths coming."
Romance
The profile of Rowling reveals that she sketched out the plots for all seven books long ago.
She promises dramatic developments - "there's at least one death that's going to be horrible to write" - including more romance.
Rowling said that more "more boy-girl stuff" was inevitable: "They're 15 now, hormones working overtime.
"Harry has to ask some questions, that I hope the reader will think: 'Well, why hasn't he asked this before?'"
Film
Harry has already been interested in a "quidditch" team-mate in Harry Potter And The Goblet Of Fire, the fourth book in the series - but will now develop more of an interest in Hermione, one of his best friends.
The film of the second book, Harry Potter and the Chamber of Secrets, is already in production and scheduled for release in the middle of next year.
The four Potter novels so far have sold more than 100 million copies, while the movie is breaking box-office records worldwide.
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