Kristen Stewart's casting as Princess Diana was announced in June 2020. At the time, director Pablo Larraín told Deadline that the actress was "one of the great actors around today." He added, "To do this well, you need something very important in film, which is mystery. Kristen can be many things, and she can be very mysterious and very fragile and ultimately very strong as well, which is what we need. The combination of those elements made me think of her."
"The way she responded to the script and how she is approaching the character, it's very beautiful to see," he continued. "I think she's going to do something stunning and intriguing at the same time. She is this force of nature."
The film is based on real-life events. Spencer, which is Diana's maiden name, takes place in December 1991, when she and Prince Charles spent a Christmas holiday with the royal family at one of Queen Elizabeth II's additional residences, in Sandringham, England. That weekend, she made the decision to leave her husband, following much relationship turmoil. The two ultimately divorced in August 1996 after 15 years of marriage.
"We decided to get into a story about identity, and around how a woman decides somehow, not to be the queen," Pablo Larraín told Deadline in June 2020. "She's a woman who, in the journey of the movie, decides and realizes that she wants to be the woman she was before she met Charles."
Spencer is set for release in fall 2021.
It was confirmed in March 2021 that Jack Farthing was cast as Prince Charles, Diana's husband. He is known for roles in the BBC drama series Poldark and the network's comedy Blandings. He also appeared with Olivia Munn in the Netflix movie Love, Wedding, Repeat.
German model Olga Hellsing will make her acting debut as Sarah "Fergie" Ferguson, the Duchess of York and now ex-wife of Prince Charles' brother Prince Andrew, Deadline reported in March 2021.
British-German actor Thomas Douglas will play Diana's father, Earl John Spencer, Deadline reported in March 2021. He previously appeared in the 2020 miniseries Labyrinth of Peace and the crime series Tatort, Germany's longest-running TV drama.
Timothy Spall, who played Wormtail in the Harry Potter films and also starred with Jack Farthing on the comedy show Blandings, The Shape of Water and Blue Jasmine actress Sally Hawkins and Mission: Impossible movie series star Sean Harris also appear in Spencer, Deadline reported in January 2021.