A rare signed first edition of Harry Potter and the Philosopher's Stone has been sold for £19,700 at Christie's auction house in London.
Another first edition of the book sold for £9,000 earlier this year
Experts had estimated the book, which was signed "Joanne Rowling", to have been worth between £8,000-£12,000.
The auction also included a publisher's proof copy of the book.
The misspelling of JK Rowling's name on the title page as "JA Rowling", did not deter bidders and the manuscript sold for £2,250.
A signed paperback edition, also inscribed by Rowling, was sold along with a similarly inscribed first hardback edition of the second book in the series - Harry Potter and the Chamber of Secrets - for £1,250.
The message in the first book said: "To Ella - I know your Mum!!! And she beat me in the quiz but we won't mention that - love from Jo (aka JK Rowling)".
The seventh Potter book broke sales records on both sides of the Atlantic when it was published in July, selling 11 million copies in 24 hours.