Dame Maggie Smith completed filming this movie while undergoing radio-therapy as treatment for breast cancer.
Hero Fiennes Tiffin was cast as Tom Riddle, age eleven, while his uncle, Ralph Fiennes played Lord Voldemort (formerly Tom Riddle). His parents are Martha Fiennes (Ralph's sister) and George Tiffin. Director David Yates says that he hired Hero because of his resemblance to his uncle, but not specifically because he was the actor's nephew. He liked the dark haunted quality about the young actor.
Horace Slughorn's (Jim Broadbent) outfits were designed to look very rich and elegant, but also old and threadbare. The costumes were distressed to make them appear worn, and in addition, were washed in a powdery solution to make them appear as if they had gathered dust during the years of Slughorn's retirement.
Daniel Radcliffe's least favorite own performance in the franchise, stating in an interview in 2014 that he was "just not very good in it", and calling it "hard to watch". He also revealed that he was struggling with alcohol at the time of filming and can tell in certain scenes that he was intoxicated.
Robert Knox (Marcus Belby) was tragically stabbed to death on May 24, 2008, just a few days after filming wrapped.