Rumors that Gaga would be joining the Joker universe first surfaced in June, with The Hollywood Reporter suggesting that she'd be playing a new incarnation of Harley Quinn — the Joker's murderous girlfriend who is currently portrayed by Margot Robbie in the DC Extended Universe and Kaley Cuoco on HBO Max's beloved animated series. While the House of Gucci star didn't confirm those reports in her Twitter post, the teaser closes with an image of Phoenix and Gaga dancing... well, cheek to cheek. That certainly suggests a Joker and Harley love connection.

The Joker 2 teaser drop arrives as Warner Bros. Discovery seeks to move on from the messy fallout surrounding the sudden shelving of Batgirl, a nearly-completed HBO Max feature that would have starred Leslie Grace as the titular heroine and Michael Keaton as the version of Batman who first hit the big screen in 1989. Grace recently commented on the decision, praising the movie's cast and crew and thanking fans for their support. "THANK YOU for the love and belief, allowing me to take on the cape and become, as Babs said best, 'my own damn hero!' #Batgirl for life!"
When Joker premiered in 2019, both Phillips and Phoenix indicated it would be a one-off experiment. But after the film cleared the billion-dollar mark at the worldwide box office and won its star a Best Actor statue, a sequel became inevitable. According to The Wrap, Joker: Folie à Deux — which refers to the psychiatric condition known as "shared psychosis" — will take place largely in Arkham Asylum, where Phoenix's Clown Prince of Crime was locked up at the end of the original film. In DC Comics lore, Arkham is also where the Joker first encounters psychiatrist, Dr. Harleen Quinzel, who later becomes Harley Quinn.

Gaga's surprise announcement is already bringing together music and comic book fans on Twitter.