"I've written other things during that time, but on and off for five years, that's been my priority," Rowling, 47, said in an exclusive and rare interview for television with "Nightline" co-anchor Cynthia McFadden in Edinburgh, Scotland. "I think I've been surprised by the fact that Harry hasn't left me to the degree that I thought he would. And I'm quite glad about that."
Rowling's Potter books have been published in 73 languages, sold more than 450 million copies, spawned popular film spin-offs, and made her the first billionaire author.
The frenzy around this new book, her first aimed solely at adults, has led the publisher to guard it like a state secret, protecting the plot until its Sept. 27 release date. (ABC News producers read the manuscript, kept under lock and key in the publisher Little, Brown and Company's New York office).
Fans thinking that the world in Rowling's new book relates in any way to the magic of her Harry Potter universe are in for quite a surprise.
Set in a seemingly idyllic British town of Pagford, the story starts with the sudden death of local man, Barry Fairweather, whose absence leaves a seat on the parish council, and unlocks "the biggest war the town has yet seen." Described as "blackly comic," the book is about the secrets and conflicts among the townspeople behind closed doors and explores dark topics such as adolescent sexuality, cutting and death.
"There are all of those things," Rowling said. "When I read the blurb that said it's a 'black comedy,' I thought -- that's not maybe how I would've described it. I would've maybe said it's a comic tragedy."
The book marks a new literary direction for Rowling, who has made a name for herself with her wildly popular Harry Potter series. Completely leaving her signature realm of fantasy behind, the book is grounded in the real-world and incorporates popular teen culture. The Rihanna song, "Umbrella," featuring Jay Z, plays a very prominent role in the story.
"The song's just perfect for the book because of the rap at the beginning. There's this rap that Jay Z does at the beginning of the song and it's actually a very celebratory rap," said Rowling. "It's saying, 'I'm shockproof ….I'm famous, I have money, let the Dow Jones fall, I'm OK,' and it's said in the book by a girl who doesn't really understand the words and who is not OK. It's very poignant to me that this girl doesn't understand."
Rowling has discussed her bouts with depression, even revealing that she felt suicidal in her early life. However, this is the first time she has spoken publically about her struggles as a teenager with an obsessive compulsive disorder. It was an experience, she says, that informed part of the story in her new book.
"We have an adult character in the book who has obsessive compulsive disorder [OCD]," she said, "These are things I know from the inside. … When I was in my teens I had issues with OCD."
For Rowling, the anxiety disorder manifested itself as "compulsions" – "checking, double checking, triple checking" things, she said.
As for her depression, she says it has not been part of her life for "more than a decade," attributing part of that to the tremendous success of Harry Potter.
"It cheered me up a lot. … Forget the money. Harry Potter gave me back self respect. Harry gave me a job to do that I loved more than anything else," she said. "So forget the money. Let's just say it had made just enough to justify continuing to write. It would've still cheered me up a huge amount. …. It was an amazing thing that happened."
After five years of writing and polishing the novel, Rowling will promote the book in the U.S. and Britain and then her reward will be to retreat to her home in Scotland to enjoy the quiet time she cherishes.
"I am really looking forward to us getting home because we have a new dog… so my reward is to get home and look after a new puppy while writing on the kitchen table."
For more from J.K. Rowlings, check out ABC News and Yahoo’s Newsmakers interview.