Thorne, Jack. Harry Potter and the cursed child. Parts one and two, 2016: page facing title page (based on a new story by John Tiffany) jacket flap (John Tiffany, has won multiple awards for his directing work both in the West End and on Broadway, associate director of the Royal Court, was associate director of the National Theatre of Scotland from 2005 to 2012)

Wikipedia, July 20, 2016 (John Tiffany, English theatre director, born 1971)

Internet Movie Database, July 20, 2016 (John Tiffany, director, TV and film)

Broadway World website, July 20, 2016 (John Tiffany, stage director, playwright)