Joaquin Phoenix Returns as the Joker in "Joker: Folie à Deux" Behind-the-Scenes Photos

In December 2022, Phillips revealed that "Joker 2" was in production when he shared the first photo from the sequel. Then, Lady Gaga shared a new first-look photo from the film on Valentine's Day.

Folie à deux is a French term for a rare mental disorder that's also known as shared psychotic disorder. According to the National Library of Medicine, folie à deux occurs when the delusion of one patient who suffers from a psychotic disorder is transmitted in its entirety, or in part, to someone else. The condition usually occurs with people who are in close relationships.

Will Joaquin Phoenix Play Joker in "Joker 2"?

In August 2022, Variety reported that the forthcoming movie will, indeed, mark Phoenix's return as Joker.

Who Will Play Harley Quinn in "Joker 2"?

On March 25, 2023, new behind-the-scenes photos from the movie's filming appear to confirm that Lady Gaga will be playing a new version of Harley.

Who Else Is in the "Joker 2" Cast?

News on most of the sequel's cast is still forthcoming, but in September 2022, Deadline revealed that veteran actor Brendan Gleeson — who has appeared in "Gangs of New York," the Harry Potter franchise, "Assassin's Creed," and many more films — would be joining the movie, though details on his role have not yet been revealed.

Zazie Beetz is also confirmed to return. Meanwhile, Harry Lawtey, Catherine Keener, and Jacob Lofland have joined the cast in undisclosed roles.

The plot details for "Joker 2" are being kept under wraps, and very little is known thus far. However, the teased movie title could offer some insight into the story.

The sequel's title may hint that the Joker will experience this mental disorder alongside his iconic comic-book partner in crime, Harley Quinn. While the first movie delves deep into the psyche of Arthur Fleck and shows his transformation into the violent villain, Joker, the second movie might explore his troubled on-and-off relationship with Harley as they both bring out the worst in each other.

The "Joker" sequel will hit theaters Oct. 4, 2024.

According to reports by The Hollywood Reporter, "Joker 2" is indeed set to be a musical! "Joker" as a musical, strange as it may sound, has a lot going for it.

The 2019 "Joker" movie was a massive success, netting Phoenix the best actor award at the Oscars and ultimately becoming the fourth highest-grossing R-rated movie of all time. Phillips has also worked with Lady Gaga before, producing 2018's "A Star Is Born" with Gaga and Bradley Cooper.

And while Phoenix may not seem like the most likely contender for a lead in a movie musical, he has some previous musical experience. He played Johnny Cash in the 2005 biopic "Walk the Line," doing his own singing and playing the guitar for the film. It's not too hard to imagine the Joker singing gritty, angry country ballads in Cash's trademark style, though how that would mesh with Gaga's stratospheric pop vocal chops remains to be seen.