J.K. Rowling said on Tuesday that she will miss being able to retreat into the fictional world of Harry Potter after finishing the seventh and final volume on the teen-age wizard.

But in an interview with NBC television's Today show, Rowling, 41, said it felt incredible to have completed the series she began 17 years ago when the idea came to her as she traveled on a train from Manchester to London.

At the moment it feels great to be honest with you, she said during the interview at Edinburgh Castle in Scotland. It's a really nice place to be.

It's a big sense of achievement, she said. I mean I am sad, but I think (I was) sadder immediately after finishing writing. I felt devastated. For about a week I was hard to live with after finishing this book.

The much-anticipated Harry Potter and the Deathly Hallows became the fastest-selling book in history when it was released around the world on Saturday. More than 11 million copies were sold in the first 24 hours in the United States and Britain.

I think the whole thing, it was this amazing cathartic moment, the end of 17 years' work, and that was just hard to deal with for about a week, Rowling said.

It brought back a lot of memories of what had been going on in my life when I started writing, said the mother of three who had financial difficulties when she got the idea of Harry Potter but now is estimated to be worth $1.12 billion, making her the first dollar-billionaire author.

When I started I wasn't in a bad place, then life had it's ups and downs, so Harry has been with me through a lot. I think it was that feeling more than any other, that I wouldn't have that world to retreat into again, she said.

INFLUENCE OF HER MOTHER'S DEATH

After Rowling came up with the idea, her mother died in December 1990 after suffering from multiple sclerosis for several years, which Rowling said changed both my world and Harry's forever.

The following year, Rowling moved to Portugal as an English teacher and met and married journalist Jorge Arantes, with whom she had her first child Jessica. The couple later divorced.

Rowling left Portugal for Edinburgh, where her sister Di lived. There she finished her first novel, writing most evenings and in cafes when Jessica fell asleep in her stroller.

That book, Harry Potter and the Philosopher's Stone, went on sale in 1997, winning several awards and helping earn the author a U.S. publisher.

In addition to the books, the first five Hollywood movie adaptations of her Harry Potter stories have amassed around $4 billion at the global box office. The final film in the franchise is slated for release in 2010.

In December 2001, Rowling married Neil Murray, an anesthetist. The couple have two children.

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