LONDON: Author JK Rowling confessed she was feeling sad that her days penning the Harry Potter books were almost over.

But, as ever, she steadfastly refused to reveal any plot twists in the tale of the teenage wizard when she went to a garden party for 2000 children at Buckingham Palace to celebrate the Queen's 80th birthday.

Rowling, now writing the seventh and final book in the saga that has already sold over 300 million copies, told Reuters: "I am feeling sad as it is the last one. But so far, so good."

Pressed on when the book would be ready for publication, she would only say: "I'm doing well I think. You can never really tell till you get near the end. I am not quite there yet."

Children at the palace party mobbed Rowling like a pop star wherever she went, clamoring for an autograph and then being reduced to reverent silence when she sat down to read to them extracts from the last Potter book.

Unabashed by the frenzy of young fans stretching out eagerly for a signature, she said: "This is the bit I like. I like meeting them."

At a special "author's corner" set up in a tent on the lawns of Buckingham Palace she shared a stage with Michael Bond, who penned the tales of Paddington Bear, and Philip Pullman, author of the haunting His Dark Materials trilogy.

Hailing what she called a golden age for children's literature, she said: "I think this is a fantastic way to celebrate the Queen's birthday. I think it was such a good idea. It's wonderful to see all these children here."

As Winnie the Pooh paraded round the palace gardens alongside Peter Rabbit and Toad of Toad Hall, she reflected on the bizarre backdrop.

It must have ranked as one of the weirdest places she has ever been mobbed by pint-sized fans.

"I must say it is quite surreal to be here in Buckingham Palace," she said, disappearing behind a sea of little hands waving autograph books and Harry Potter paperbacks.