And the succinct, 800-word story, written in the author's own hand, will be auctioned off for charity in London on June 10. (The tale is so shrouded in secrecy, it’s not even clear if the boy wizard makes an appearance.)
Proceeds will go to the writers' association English PEN and to Dyslexia Action.
Fans – who have gone almost a whole year since Rowling's last installment, Harry Potter and the Deathly Hallows – will be able to read the prequel for themselves when it's published by Waterstone's in August.
In her sign-off to the story (written on a piece of paper not much bigger than a postcard), Rowling said, "That was fun!"