Harry Potter author JK Rowling delighted fans by announcing Thursday - her 43rd birthday - that a book of fairy tales she penned for a charity auction and close friends will go on general release just before Christmas.

The book, The Tales of Beedle the Bard, was written after Rowling completed Harry Potter and the Deathly Hallows, her seventh and last instalment about the boy wizard.

Until now, Rowling had released only seven handmade editions of the handwritten and illustrated tales, of which she gave six to close friends and one for auction.

It was bought for 1.95 million pounds (nearly $4 million) by online retailer Amazon last December, becoming the most expensive modern book sold at auction.

"There was understandable disappointment among Harry Potter fans when only one copy of The Tales of Beedle the Bard was offered to the public last December," Rowling said Thursday.

"I am therefore delighted to announce that...The Tales of Beedle the Bard will now be widely available to all Harry Potter fans."

She said royalties would be donated to a children's charity.

The Tales of Beedle the Bard contains five stories - The Tale of the Three Brothers, The Fountain of Fair Fortune, The Warlock's Hairy Heart, The Wizard and the Hopping Pot, and Babbitty Rabbitty and her Cackling Stump.