Folie à Deux' co-star Joaquin Phoenix said she lost "a lot" of weight for it. Here's what to know about her diet and fitness routines.

Lady Gaga recently shared the movie's final trailer, and she sounds absolutely incredible singing "That's Life" in it. What we know about Joker: Folie à Deux is limited, but that'll change when it hits theaters in October.

Joker and Harley Quinn are sharing their madness with Gotham City as mayhem reigns in the trial of Arthur Fleck.

EW's exclusive clip from the "Joker" sequel shows Gaga and Phoenix passionately kissing before passing a puff of cigarette between their lips.

In a new featurette for Joker: Folie à Deux, director Todd Philips and stars Lady Gaga and Joaquin Phoneix discuss Gaga's role in the film. "She easily slipped into that world. It's not like she's trying to be Harley Quinn from the comic books. She's Lee in this world," Phillips shared.

That certainly looks to be the idea in the latest trailer for Todd Phillips all-singing, all-dancing movie with music Joker: Folie À Deux, which sees Joaquin Phoenix's Arthur Fleck taking to the stand as he goes on trial for the televised killing of Murray Franklin (Robert De Niro) in Joker.

Lady Gaga is already making naysayers eat their words with just the teaser of Harley Quinn in Joker: Folie à Deux.

Joker: Folie à Deux. The 60-second video features Lady Gaga's Harley Quinn visiting an emaciated Arthur Fleck, or Joker, played by Joaquin Phoenix, who is in a mental institution. Before she leaves, she pulls out a red lipstick and smears a clownish grin,