Apparently the Joker and Harley Quinn film is replacing what was originally David Ayer's Gotham City Sirens, which would have focused on Gotham's most iconic female supervillains: Harley Quinn The Joker: Folie à Deux title hints that Harley will be as equal of a focus as Arthur Fleck. Folie à Deux refers to a mental illness that two people share, and Joker 2 will explore that by bringing Lady Gaga's Harley Quinn into Joaquin Phoenix's Joker's life. This could allow the sequel to have a better exploration of mental illness than the This was a lot of individuals first exposure to Harley Quinn and brought in a much younger crowd which was when the idolization of the Joker and Harley Quinn’s relationship skyrocketed. On February 7 th , 2020, Harley Quinn got her first standalone movie: Birds of Prey: And the Fantabulous Emancipation of One Harley Quinn (later changed to Jared Leto and Margot Robbie are set to reprise their roles as the Joker and Harley Quinn in a new movie project, separate from the Joker origins movie by Martin Scorsese. The film is described as an “an insane and twisted love story” and is set to take place after the sequel to Suicide Squad. Told from Harley Quinn's point of view, it was important for the story that she be free, single and separate from her overbearing on-again-off-again paramour, The Joker. During CCXP, the Joker and XFQGPk.