Author JK Rowling says she expects to begin writing the seventh and final Harry Potter book by the end of 2005.
Speaking to 14-year-old fan Owen Jones, Rowling said she was "dreading" the end, although there would be "a sense of achievement" in finishing the saga.
Owen, who is from Cardiff, was the only UK person to interview the author, after winning a competition.
He spoke to Rowling at Edinburgh Castle as she launched the sixth book - Harry Potter and the Half-Blood Prince.
The interview was broadcast on ITV on Sunday.
"Even though I have known it is coming for the past fifteen years, I have known that the series would end, I think it will still be a shock," said Rowling.
The book went on sale at 0001 on 16 July
"Conversely, obviously there will be a sense of achievement... I suppose there will be some benefits to not writing Harry Potter books any more. So it is about 50-50 really."
Asked why she was so secretive about the Harry Potter plots she said it was not a marketing ploy to make money.
Rowling said: "I gain nothing but the satisfaction of knowing that all my hard work goes to the people for whom it is intended.
"In other words, people who really want to read the books, and I definitely believe that 99.9% of my readership would rather read the books and find out for themselves.
She added that she finds it hard that some people try to spoil the surprise of her books ahead of their release.
"I find it upsetting and disquieting that some elements are so keen on spoilers because it seems such a mean spirited thing to do.
"This is not about money or anything other than the pleasure of reading for people who want to read it."
Rowling, who reportedly wrote the first Harry Potter in an Edinburgh cafe, said she also finds it difficult that she can no longer be anonymous.
"One of my regrets would be that I will never again have the pleasure of sneaking into a cafe, any cafe I like, sitting down and diving into my world and no one knowing what I am doing and no one bothering about me and being totally anonymous, that was fantastic," she said.
On the subject of what she will write about when the Harry Potter adventures draw to close, Rowling said she had no idea.
"I get asked a lot whether I would write another series, I don't know because the thing that interests me about Harry Potter was not the fact that it was a series, it was just the story and the subject matter, so I could do a one-off, could do a series, I don't know."