Catherine Keener boards Joker 2

Catherine Keener is the latest star to be cast alongside Joaquin Phoenix and Lady Gaga in 'Joker: Folie à Deux'.

According to Deadline, the 'Being John Malkovich', 63, has landed a mystery role in the upcoming musical sequel to the 2019 original film.

The latest casting news comes shortly after it was revealed that Brendan Gleeson joined the ensemble.

It's also not known what role the 67-year-old Irish star will portray in the motion picture.

Gaga is taking on the role of Harley Quinn and Phoenix is back as the titular Joker aka Arthur Fleck in Todd Philips' sequel to the psychological thriller.

Zazie Beetz will also return for the second movie to reprise her 'Joker' role as Sophie Dumond.

Production is set to get underway in December, and the motion picture is slated for release on October 4, 2024.

The title of the movie is a French phrase, which translates to refer to a mental disorder that impacts two or more people.

'Joker' took home a record-breaking $96.2 million at the box office during its opening weekend. In total, it took $1.07 billion internationally, making it the highest ever grossing R-Rated movie.

Phoenix and Hildur Guonadottir took home Academy Awards, for Best Actor and Original Music Score, respectively.

Overall, the film was nominated for 11 Oscars, including the top prize, Best Picture, and Best Director for Phillips.

In June, it was revealed Gaga was in early talks to star in the 'Joker' sequel in the role of Harley Quinn, who was played by Margot Robbie in the 2016 and 2021 movies 'Suicide Squad' and 'The Suicide Squad'. The character has an on/off abusive relationship with Joker.

Phillips has been working on the script for the sequel with Scott Silver, with whom he co-wrote the first movie alongside.