The film, which refers to the French term for “madness of two” – when two people in an intimate relationship share elements of the same mental illness, such as delusions – will see The Joker and Harley fall in love at Gotham City’s Arkham Asylum.

Speaking about the film, Lady Gaga said: “My experience with the character was really, really personal.

“When we were making the movie constantly discovering new things on set, through dance, through costumes, through make-up, through the story.

“I was really honoured to produce it.”

It comes after the US singer announced she would be releasing a 13-track “companion” album to the film named Harlequin on Friday.

Lady Gaga mirrored her character at the event at the Cineworld cinema, wearing a red dress – in a nod to Harley Quinn’s signature colour – and extravagant make-up, featuring blue eyeshadow and a red lip.

The sculpted jacket and gown with a low-cut neckline and asymmetric skirt was a custom Celine design, with her mixed black-and-red chopped wig aiding the method dressing.

She was joined at the premiere by director Todd Phillips, who said the film aimed to show that The Joker “had music inside of him”.

He told the PA news agency: “We just thought, well what happens if he (The Joker) finally has love in his life?

“Maybe that music that’s inside of him comes out of him, and so to us, it seemed rather logical.

“The most challenging thing was like, oh, wait a minute, we’re really going to do this and, you know, Joaquin is not a naturally trained singer, although I’m of the firm belief that Joaquin Phoenix can do anything.

“He was very intimidated by it, so it was cool.”

The film, which is the sequel to the 2019 movie Joker, will be released in cinemas across Ireland on Friday, October 4th.