Why so valuable? J.K. Rowling’s handwritten notes made this rare first edition unique. (Matt Dunham/AP)

A unique first edition of “Harry Potter and the Philosopher’s Stone,” with notes from author J.K. Rowling, has sold for a record $227,421 at a London charity auction.

The 1997 book, featuring handwritten notes, 22 original illustrations and a 43-page “second thoughts” commentary by the author, sold for the highest price to date for a printed book by Rowling, auction house Sotheby’s said.

Sotheby’s said the sale room fell silent on Tuesday as buyers engaged in a bidding war for the book. The new owner, who bid by telephone, was not identified.

The Harry Potter book was one of 51 first editions in the auction. Others included a copy of Roald Dahl’s “Matilda,” with new illustrations by Quentin Blake. The money raised went to charity.

Only 500 first editions of “Harry Potter and the Philosopher’s Stone” exist, making them the rarest of the series. The book was renamed “Harry Potter and the Sorcerer’s Stone” when it was released in the United States.