Comic Relief co-published J.K. Rowling’s 2001 companion book Quidditch Through the Ages.
The book was presented as a Hogwarts library volume written by the fictional author Kennilworthy Whisp. In reality, Rowling wrote it as a charity publication, and proceeds supported Comic Relief. The text describes the history, rules and development of Quidditch, the broomstick sport played by witches and wizards in the Harry Potter universe.
Its humorous framing makes the book look like an in-world reference work. Harry’s name appears in the borrowing information, which helps connect the fictional library copy to the events of the novels. The work is not a conventional narrative sequel and does not continue Harry’s plot.
The other principal 2001 charity companion title was Fantastic Beasts and Where to Find Them. That book is attributed in-world to Newt Scamander and discusses magical creatures. Both publications were sold to raise money, but Quidditch Through the Ages was associated with Comic Relief.