State the obvious: Lady Gaga is an astonishing singer. And while her hit-packed back-catalogue speaks for itself, she’s also brought those considerable pipes to the cinema screen in A Star Is Born, the reigning pop-icon playing pop-icon-in-waiting Ally. Next up in her cinematic arsenal, after serving killer looks in House Of Gucci, Gaga is about to sing on screen again – this time as an all-new take on Harley Quinn in Todd Phillips’ song-packed Joker sequel, Joker: Folie À Deux. Get ready to meet Lee – Arthur Fleck’s new partner in crime, set to put a spring in his step and a song in his heart.

For Gaga, the film’s song-and-dance numbers required a recalibration of her vocal talents. “People know me by my stage name, Lady Gaga, right? That’s me as that performer, but that is not what this movie is; I’m playing a character. So I worked a lot on the way that I sang to come from Lee, and to not come from me as a performer,” she tells Empire in the world-exclusive Joker: Folie À Deux cover feature. And given how Phillips’ film integrates music into its milieu, Gaga had to follow suit. “How do you take music and have it just be an extension of the dialogue, as opposed to breaking into song for no conceivable reason?” she asks. “It was unlike anything I’ve ever done before.”

As a result, you’re about to hear a very different side to the Lady Gaga you know. “For me, there’s plenty of bum notes, actually, from Lee,” she laughs of her singing in the film. “I’m a trained singer, right? So even my breathing was different when I sang as Lee. When I breathe to sing on stage, I have this very controlled way to make sure that I’m on pitch and it’s sustained at the right rhythm and amount of time, but Lee would never know how to do any of that. So it’s like removing the technicality of the whole thing, removing my perceived art-form from it all and completely being inside of who she is.”

In Gaga’s hands, get ready for an all-new take on a fan-favourite character – one who’s thrived in Batman: The Animated Series, comic books, the DCEU, and her own animated comedy. Lee is both the Harley Quinn you know, and one you really don’t. “While there are some things that people would find familiar in her, it’s really Gaga’s own interpretation, and Scott [Silver, co-writer] and I’s interpretation,” explains Phillips. “She became the way how [Charles] Manson had girls that idolised him. The way that sometimes these [imprisoned murderers] have people that look up to them. There are things about Harley in the movie that were taken from the comic books, but we took it and moulded it to the way we wanted it to be.” Prepare for a performance that’s totally Gaga.

There have been all kinds of iterations of the Joker over the years. Some veered more towards the exaggerated mobster route, like Jack Nicholson in Tim Burton’s Batman; there was Heath Ledger’s nihilistic terrorist in The Dark Knight; Jared Leto’s eccentric tattooed gang leader in Suicide Squad. But in Joker, Joaquin Phoenix gave us a totally different conception of who Batman’s arch-nemesis might be – a lonely, disenfranchised failed comedian whose inner turmoil spills over into violent acts that bring out the darkness festering in Gotham City. In Todd Phillips’ film, Arthur Fleck wasn’t a villain, let alone a maniacal schemer – more a mercurial, unpredictable force moving through the world in his own unique way.

And so, in Joker: Folie À Deux – the much-anticipated sort-of-sequel that sends Fleck to Arkham, where he’ll strike up a music-fuelled relationship with Lady Gaga’s Harley ‘Lee’ Quinzel – we’ll be venturing further into Arthur Fleck’s psyche. But, in keeping with the previous film, it won’t see the Joker become Gotham’s Clown Prince Of Crime. “We would never do that,” Phillips explains to Empire in the world-exclusive Joker: Folie À Deux cover feature. “Because Arthur clearly is not a criminal mastermind. He was never that.” While Fleck isn’t angling to become a criminal figurehead in Arkham, the world is watching him. “Arthur has become this symbol to people,” Phillips says. “This unwilling, unwitting symbol now paying for the crimes of the first film, but at the same time finding the only thing he ever wanted, which was love. That’s always what he’s been about, even though he’s been pushed and pulled in all these directions. So we tried to just make the most pure version of that.”

That purity of character exploration dovetails with Folie À Deux’s most unexpected stylistic swing – that Fleck (and Gaga’s Lee) will break into song. It comes from the notion in the first film that, in Phillips’ words, Fleck “has music in him”. Cue Phoenix singing showtunes, as channelled through Arthur. “It was important to protect that with poor phrasing and occasional bum notes,” the actor tells Empire. “Arthur grew up hearing his mother play these songs on the radio. He’s not a singer, and he shouldn’t sound like a professional singer. He should sound like somebody that’s taking a shower and just bursts out into song.”

He was, however, performing opposite the professional singer, Lady Gaga. “I do seem to remember her spitting up coffee the first time I sang, so that felt good, that was exciting, and made me feel confident,” he jokes. Together, they found a creative harmony. “Gaga was always very encouraging of just, ‘Go with what you feel, it’s fine’,” says Phoenix. “For somebody who’s not a performer in that way, it can be... uncomfortable to do that, but also very exciting.” Prepare for one hell of a cinematic duet.