Director Bertrand Bonello started writing the screenplay in 2017 with Gaspard Ulliel and Léa Seydoux in mind for the lead roles, after having worked with both actors in Saint Laurent (2014). The project was officially announced in January 2021, but filming was postponed due to the COVID-19 pandemic and was scheduled to start in April 2022. In the meantime, Bonello directed the film Coma (2022) instead, which featured Ulliel in the last movie he filmed and the last work he finished. Ulliel passed away on January 19, 2022 following a skiing accident, and the filming for 'The Beast' was delayed again. In February 2022, Bonello told Variety that he would likely recast Ulliel's role with a non-French actor. On May 16, 2022, it was announced that British actor George MacKay was cast as the male lead and that filming was scheduled to start in August 2022.
The movie was briefly shot in Los Angeles without permission.
It was rejected from the 2023 Cannes Film Festival, but ended up being selected for the 2023 Venice Film Festival.
Freely inspired by the 1903 novella "The Beast in the Jungle" by Henry James. After the first scene, the movie starts pretty much the same as the novella, but diverges quickly afterwards. For the parts that are similar to the novella, the main change is that the two main characters are gender-swapped.
Director Bernard Bonello wanted a non-French actor to replace recently deceased Gaspard Ulliel, so that the actor would not suffer from the comparison with Ulliel. A British actor, George MacKay, was hired, but he did not speak French at all, so he learned it just for the role, thus confirming in Bonello's eyes the English actors' reputation of being hard workers.