J.K. Rowling read through the script for this film, and found a line where Dumbledore mentions a girl he had a crush on when he was younger. After reading it, she informed the filmmakers that Dumbledore is in fact gay, and that his only romantic infatuation was with the wizard Grindelwald, whom he later had to defeat in a wizard duel. She later made this information public while promoting the final book, Harry Potter and the Deathly Hallows.
Helen McCrory had been cast to play Bellatrix Lestrange in Harry Potter and the Order of the Phoenix (2007), but had to back out because she was pregnant. She will play Bellatrix's sister, Narcissa Malfoy in this film.
Jessie Cave beat over 7000 girls to win the role of Lavender Brown, Ron's "love-interest" from the book.