Despite the massive box office success of Joker, director Todd Phillips said he was anxious to approach the sequel, which premiered at the Venice Film Festival Wednesday.
The first film won the Golden Lion and brought in more than $1 billion. The second, Folie i Deux, follows Arthur Fleck (Joaquin Phoenix) as he falls for Harleen Quinzel, better known as Harley Quinn (Lady Gaga).
"If you remember the first film Arthur has a musicality to him," said Phillips. "He is often dancing to express the way he feels. And Hildur Gui°nadottir's score is almost a character in the first film. So when it started taking shape with actual music elements we thought what if we got Lady Gaga who actually brings music with her."
Lady Gaga said that the movie's music allowed the characters to be more completely expressed.
"Stefani (Lady Gaga) said early on that we're singing live and I said no we're not. And then we did," Phoenix said. "Not only did we sing live, but every part of the recording was live. Each take was a different version of the song and that felt really exciting."Joker: Folie i Deux premieres Oct. 4.