LAS VEGAS – Joaquin Phoenix danced down stairs and showcased a little soft-shoe when he wasn't murdering people in the first "Joker." Now, he and his new co-star Lady Gaga have just gotta sing in the sequel.

Director Todd Phillips showcased a first look at his new musical psychological thriller "Joker: Folie à Deux," which again stars Phoenix as unhinged comedian-turned-criminal Arthur Fleck, aka Joker, and introduces Gaga as his love interest, Harleen Quinzel (better known as Harley Quinn), who appears to be a fellow inmate. After teasing fans earlier Tuesday with a brief clip of Fleck laughing hysterically in a downpour, Phillips premiered the first trailer during a Warner Bros. panel at CinemaCon, the annual convention for theater owners and studios.

The trailer finds Arthur in Gotham City’s Arkham Asylum, imprisoned for his crimes. He meets Harley, who’s already a fan: “I’m nobody. I haven’t done anything with my life like you have,” she tells him. She wants them to break out, and the rest of the footage shows them on the loose but also dancing and singing in fantastical musical numbers. (Like the first movie, there looks to be a blending of the real and the imaginary.)

But during his CinemaCon presentation, Phillips pushed back against the new “Joker” being considered a conventional “musical.” “We’ve never talked about it like that. It’s a movie where music is an essential element,” he said. The director and Phoenix talked about the fact that in the original "Joker," “Arthur is weird and aloof, but he has music in him. He has grace in him. It didn’t seem like that big a step to what we do here.”

The Joker's wild evolution in photos:From Jack Nicholson to Joaquin Phoenix

The first "Joker" was a chilling origin story that polarized critics but hit big at the box-office: It became the first R-rated movie to gross more than $1 billion and was the sixth highest-grossing film worldwide in 2019. Phillips' next chapter changes things up by embracing musical elements as it retells the DC Comics "love story" – or, to quote a Gaga tune, one seriously bad romance – between Joker and Harley.

Phoenix won a best actor Oscar in 2020 for his portrayal of the iconic supervillain in the first "Joker," which was also nominated for best picture. Gaga is the second actress to portray a live-action Harley Quinn on the big screen, following Margot Robbie.

"Joker: Folie à Deux" is expected to arrive in theaters Oct. 4. The cast features a returning Zazie Beetz as well as Brendan Gleeson, Catherine Keener and Steve Coogan.