Harry Potter author JK Rowling has exclusively told Newsround how relieved she felt when she watched the film of her first book - and liked it!

"When I actually sat down to see the film, I was terrified. Because it was way too late if bits were wrong. But at the end of the film I was happy."

She added: "I think the fans of the book will be happy. There is an awful lot of my book up there. All the important bits, I'd say."

Secrets revealed
JK also revealed she gave some of the actors some top secret background information that will emerge for the rest of us in later books.

She said she thought it was important to tell them so they knew their characters better: "I did give certain information to Robbie Coltrane, the background story about Hagrid and I gave Alan Rickman a little bit on Snape," she told Newsround's Lizo Mzimba.

"But no-one should go out and kidnap them because they won't talk!"

Quidditch
But she also said that anyone hoping to get clues about the fifth book from the film will be disappointed.

JK said she loved the film's Quidditch sequences.

"I couldn't imagine how they were going to do it, but they have, and it looks so real."