LOS ANGELES − Lady Gaga has shared how a scenic drive through Montana in late 2022 with her partner, Michael Polansky, sparked her creativity for a unique love story in the upcoming Joker film.

Polansky, who works in San Francisco, isn’t part of the Joker narrative. Gaga, 38, happily sports a large diamond engagement ring from her fiancé during her discussion. The road trip through Wyoming and the Teton Range greatly inspired her portrayal of Harley Quinn, the well-known love interest of Joaquin Phoenix’s Joker in the eagerly awaited sequel to 2019’s “Joker.”

“As Michael and I drove through the stunning mountains, I thought, ‘Can you believe this woman tells the Joker, “We’re going to build a mountain together?” She genuinely believes in that fantasy,’” Gaga reflects.

“Joker: Folie à Deux” (hitting theaters Friday) centers around a blend of dark themes and a love story, making it an unconventional musical featuring two of Hollywood’s most captivating actors. Viewers shouldn’t expect typical superhero antics or confrontations with Batman from this film, which spotlights the characters Joker (played by Arthur Fleck) and Harley Quinn (Lee Quinzel), both from troubled backgrounds.

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Although it wasn’t disclosed earlier, Phoenix and director Todd Phillips had been brainstorming the idea of a sequel to their acclaimed R-rated “Joker.” This was solidified by the first film’s success, which grossed over $1 billion, earned 11 Oscar nominations, and clinched two wins, including Best Actor for Phoenix. In this follow-up, however, they aimed for something beyond typical comic book narratives.

“We didn’t want a straightforward continuation where he’s simply out robbing banks as the Joker,” Phoenix states. “That was off the table.”

Instead, Phillips and Phoenix delved into exploring a relationship dynamic, questioning what it means to fall for a persona.

“What do you feel when someone loves the image you show the world?” Phoenix contemplates. “There was something compelling about that, especially since Arthur remains enigmatic and above it all, even after his arrest in the original film.”

“Folie à Deux” takes place two years after a film about the Joker’s notorious rampage and examines Arthur’s disillusionment with the fame of his monstrous alter ego. Phoenix’s characterization draws inspiration from the real-life struggles of the 1970s rock band KISS, envisioning what happens when the glitz fades.

“Ever think about Gene Simmons from KISS? In his 20s, fans are painting their faces and he’s rocking out. But what happens when he’s in his 40s, tired of the makeup? That thought made me laugh,” Phoenix remarks. “Todd and I realized this could spark something meaningful.”

In this follow-up, the challenges of being in the violent offenders unit at Arkham State Hospital take a toll on Arthur. His striking weight loss from the previous film is even more striking, emphasizing his deteriorating condition as he emerges gaunt and haggard from his cell.

“That was my first day on set, and I felt very diminished,” Phoenix admits. “I definitely was thinner than the first film.”

“That’s not computer-generated; that’s simply his physique,” Phillips notes about Phoenix’s appearance. “We discussed him maintaining his weight, as I didn’t want him to be unhealthy. Yet, he insisted that Arthur needed to appear a certain way. Its authenticity was crucial for him. If Arthur was gloomy before, now he’s at an even lower point.”

Following the triumph of ‘Joker,’ Joaquin Phoenix and Lady Gaga found themselves under intense scrutiny during filming

Arthur’s gloomy outlook transforms the moment he encounters Lee in “Folie à Deux” (a French term referring to a shared delusional disorder between two individuals). Once Phillips and Phoenix decided to make the sequel a fantasy musical, Gaga emerged as the obvious choice for the role, partly due to Arthur’s memorable dance scenes in the original “Joker.”

According to Phillips, directing two major stars like Phoenix and Gaga (whose real name is Stefani Joanne Angelina Germanotta) brought its own challenges, particularly with the media frenzy and high expectations from fans.

“It was challenging, but not because of their personalities,” Phillips explains. “During the first ‘Joker,’ we operated quite discreetly. With Lady Gaga involved, everything is under a microscope now.”

Gaga kicked off her role by performing a cover of “Gonna Build a Mountain,” which will appear on her upcoming “Harlequin” album and also inspired a dreamy waltz between her and Phoenix that ultimately turns into a chaotic dance.

“I was thrilled to propose the scene idea to Todd and Joaquin,” Gaga says. “It starts in the spirit of Fred Astaire and Ginger Rogers, imagining the wildest scenario where they view themselves as the epitome of joy and wellness. However, that illusion shatters. The waltz becomes chaotic, just like they are.”

The sequel features an electrifying televised trial for the Joker, where Arthur returns to his humorous, flamboyant identity, motivated by Harley Quinn’s transformation. Nonetheless, this is just a piece of the comic-book action. The performances of classic songs and the choreography highlight the dedication to crafting a unique musical experience.

It’s clear that Gaga is fully immersed in this world, even moderating her vocal performance to make Lee’s singing sound more believable. Phoenix, known for his role in “Walk the Line,” has experience in music and dance as well. However, each elaborate musical number required extensive training weeks, leading Phillips to emphasize, “There’s no CGI, no face replacement, and no stand-in for this guy.”

A full tap dance sequence for the Joker needed two hours of practice every day “for months,” according to Phoenix, adding that this part is only in the movie for about 27 seconds. “But it’s incredibly intricate,” he notes.

During training, choreographer Michael Arnold showed Phoenix the tough tap “toe stand” move, which involves balancing on one toe.

“When I attempted it, I hesitated,” Phoenix admits. “I was worried about injuring my ankle.”

In moments when he was alone and relaxed, Phoenix discovered he could indeed perform the move. While filming a scene with a vibrant Gaga at the piano, he felt a burst of inspiration and decided to go for the toe stands.

“Seeing Stefani give her all, with her muscles straining as she sang, motivated me,” Phoenix recounts. “I thought, ‘I have to attempt it on camera, even if I stumble.’ So I went for it. I couldn’t believe I actually did it. Both Stefani and I were swept away by the moment.”