Joker: Folie à Deux's cast keeps growing as Catherine Keener joins the ensemble in an undisclosed role. According to Deadline, Keener is being added as a main cast member, although we don’t know yet who she’ll be playing in the musical sequel to Todd PhillipsJoker.

Keener was last seen in The Adam Project, a sci-fi Netflix movie starring Mark Ruffalo and Ryan Reynolds. She was also recently a part of Netflix’s creepy horror series Brand New Cherry Flavor. So, Keener has plenty of experience both with blockbusters and production filled with weird elements, and Joker: Folie à Deux is both, as the sequel reportedly takes place in Arkham Asylum, the iconic Gotham City institutional to the criminally insane where all the main Batman villains go after being caught by the World’s Greatest Detective.

While Joker doesn’t feature Batman, the film’s closing scene does take place in Arkham Asylum, where Arthur Fletcher, aka Joker (Joaquin Phoenix), is sent after starting an insurrection in Gotham City and killing people live on TV. The sequel will also star Lady Gaga as Harleen Quinzel, the psychiatrist who’s charmed by the Joker and becomes a super villain herself. So, with Joker: Folie à Deux expanding Phillips’ corner of the Batman universe, we can hope to see other classic villains showing up in the sequel. If that’s the case, Keener could take on the role of one of the members of Batman’s rogues gallery.

Joker joaquin pheonix social featured

Image via Warner Bros.

RELATED: 'Joker 2' to Feature "Complicated Musical Sequences"

Keener is not the only new cast member to join the sequel. Recently, Joker: Folie à Deux also added Brendan Gleeson in a mysterious role. Zazie Beetz is also in talks to reprise the role of Sophie, Arthur’s neighbor with whom he has an imaginary relationship.

There’s still no information about the sequel’s story, besides that it is supposedly a musical film with complicated numbers. That’s one weird path to follow after Phillips’ first film stuck so close to classics such as Taxi Driver to create a gritty and realistic version of Gotham City, where the lack of access to public health can create real monsters. However, we are very intrigued by a musical set in the Batman universe and can’t wait to take a peek at Joker: Folie à Deux. Unfortunately, we shouldn’t get any new information for a couple of months yet, as the sequel only starts shooting this December.

Joker is currently streaming on HBO Max. Joker: Folie à Deux is scheduled to hit theaters on October 4. Check out the movie's only short teaser below.