Lady Gaga in talks to join Joker musical sequel as Harley Quinn alongside Joaquin Phoenix

You can't read Lady Gaga's Joker face — but you might be able to hear her powerhouse vocals in an upcoming sequel to Todd Phillip's 2019 blockbuster.

The Oscar-winning A Star Is Born actress is in talks to appear opposite Joaquin Phoenix — who is deep in his own negotiations to return — as Harley Quinn in a Joker sequel at Warner Bros., an inside source tells EW. What's more, the source says the sequel is also a musical.

As for where that leaves Margot Robbie, who's played a fan-favorite version of Quinn across several titles since 2016, the source says the role is not being recast, rather the sequel is set in an entirely different universe with different characters. The Hollywood Reporter first broke the news of Gaga's involvement in the musical follow-up on Monday.

Phillips teased the sequel in early June by posting a photo of a script titled Joker: Folie à deux on Instagram. Phillips and Scott Silver were credited as writers on the title page. Phillips also posted another image of Phoenix reading the screenplay.

In English, the subtitled phrase translates to "shared psychosis," and often refers to a psychiatric syndrome involving delusions being transmitted between two people — such as the Joker and Quinn, perhaps.

Quinn is often portrayed as a psychiatrist at Gotham City's Arkham Asylum, where she meets and falls in love with the Joker. Phoenix, however, reinvented the character with Phillips for the 2019 film, which followed the nefarious figure's origins as Arthur Fleck, a struggling clown and aspiring stand-up comic who sends the city into a spiral of violence. It became the first R-rated film to cross the $1 billion mark at the global box office.

Hear more on all of today's must-see picks on EW's What to Watch podcast, hosted by Gerrad Hall.

Related content:

• Joker director Todd Phillips teases sequel with photo of script subtitled Folie à deux
• Bullet Train director explains why Lady Gaga role didn't work out
• David Fincher says Joker was 'a betrayal of the mentally ill,' slams major Hollywood studios