The first trailer for Joker: Folie à Deux, the musical sequel to Joker starring Joaquin Phoenix and Lady Gaga, was released by Warner Bros Pictures on Wednesday.

The sequel sees Phoenix return as Arthur Fleck and Lady Gaga as Dr Harleen Quinzel, a psychiatrist assigned to treat Fleck at Arkham Asylum. She falls in love with him and becomes his accomplice Harley Quinn, according to the comic book.

The title is a reference to a psychiatric syndrome in which a delusional state is shared by two people.

Joker: Folie à Deux will be a musical and is expected to include 15 numbers, Variety reported, with most of them being covers of pre-existing songs. The trailer features the 1965 song What the World Needs Now Is Love.

Joker made box office history when it was released in 2019, becoming the first R-rated film ever to gross over $1 billion.

The 2019 movie offered a dark, R-rated origin story for Batman’s future nemesis Arthur Fleck, and polarized audiences by presenting its murderous villain as a hero, even prompting fears it could inspire mass shootings.

Introducing a new trailer for the film at CinemaCon on Tuesday in Las Vegas, movie director Todd Phillips called his latest work “a movie where music is an essential element,” adding that it “doesn’t really veer too far from the first film” in that sense.

“Arthur is weird and aloof and distant, all these things, but he has music in him, he has a grace to him,” explained Phillips.

“That informed a lot of the dancing in the first film… so it didn’t seem like that big of a step, what we did here.

“It’s different but I think it’ll make sense once you see it.”

The trailer showed Phoenix’s Joker meeting Gaga’s Harley Quinn in an asylum, before the two seemingly plot their escape.

(With input from AFP)