Which Harry Potter companion book did J.K. Rowling publish under the name Kennilworthy Whisp?

J.K. Rowling published Quidditch Through the Ages under the fictional name Kennilworthy Whisp.

The book is presented as a history of the wizarding sport of Quidditch. Its fictional author, Kennilworthy Whisp, is described as a Quidditch enthusiast and writer, allowing the work to read like an in-universe reference book rather than a conventional narrative. Rowling wrote the text outside the story world and used the fictional byline as part of the joke.

The book was published in 2001 alongside Fantastic Beasts and Where to Find Them. The two charity editions were credited to fictional Hogwarts library authors and raised money through Comic Relief. Quidditch Through the Ages discusses the sport’s development, equipment, rules, teams, and famous players. It is distinct from Fantastic Beasts, which is framed as a textbook by Newt Scamander.