US singer and actress Selena Gomez joined her co-stars on the red carpet at the London Film Festival on Friday, for the UK premiere of her Oscar-tipped film Emilia Pérez.

The Spanish-language musical was one of the breakout hits of the Cannes Film Festival earlier this year, where Gomez and three of her co-stars were jointly named best actress.

The others - Zoe Saldaña, Adriana Paz, Karla Sofía Gascón - appeared alongside Gomez in London, where the film hopes to continue its momentum in the awards race.

Emilia Pérez follows a Mexican Cartel leader (played by Gascón), who asks a high-powered lawyer named Rita (Saldaña) to help him fake his own death.

But the reason he wants to retire and disappear from the world of crime isn't what you might expect - the cartel leader wants to change gender and live a new life as a woman.

The rest of the film focuses on four women, including the newly-transitioned Emilia Pérez, as they each pursue their own version of happiness in modern-day Mexico.

Pérez is portrayed by Spanish trans actress Gascón, who has been tipped as a possible best actress contender in the forthcoming awards race.

Gomez plays the drug lord's wife, who is kept in the dark about her former lover's new identity, while Paz portrays Emilia's new romantic interest after transitioning.

All four of the film's stars walked the red carpet ahead of the film's UK premiere at the Royal Festival Hall as part of the London Film Festival on Friday.

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French director Jacques Audiard came up with the idea for the film after reading a chapter in Boris Razon's 2018 novel Écoute about a drug lord who changes identity.

Audiard went one step further for the film, and made it a story of changing gender.

"I was less interested in a change of identity to evade competitor drug barons, and more interested in the change of identity for the sake of the person she was and is,” the director told BBC News. "I was more interested in the past and what led to that transition."

The role required someone very specific – a trans actress, who was a Spanish speaker, who could also sing and dance.

Recalling the casting process, Gascón tells BBC News: “I was contacted when I was in Mexico by a production team, and was told 'We need an actress as crazy as you - you're the only one who can do this role, but you need to learn five songs for tomorrow!'

“And I was like 'OK, let's record the whole album and we'll go on tour as soon as you want!’" she joked. “But I did say, ‘this is going to be difficult, I'm not a singer'. But the team in the film, they worked with me incredibly, they really helped me with all the songs and made it so that we could do the best work possible.”

Asked about Gascón's casting, Audiard added simply: “Without her there would be no film.”

Interestingly, the actress campaigned to play both the male and female roles – in other words, the character both before and after transition.

Audiard had originally intended for a different actor to play the male drug lord Manitas, because, the director explained, he was "uncomfortable asking [Gascón] to revisit something she was moving away from".

But, Gascón recalled: “I said to Jacques, I want to play this role in the complete arc, because for me it is important to do the full part. It wouldn't be the same film if another actor played [Manitas]."

That meant using effects and make-up such as a fake beard, she explained, so she could play the drug baron in the first section of the musical.

"This film is this film because the same actress played the complete performance," Gascón continued. "It's that kind of role you have once in your life and I didn't want to lose the opportunity to play this.”

Reviews of Emilia Pérez, which is released on Netflix next month, have been generally positive so far.

"It's a wild, gritty, glitter-soaked ride that defies convention and classification," said Entertainment Weekly's Maureen Lee Lenker.

She praised the film's performances, commenting: "Selena Gomez is a welcome surprise, shedding any remaining hints of her Disney Channel origins in her portrayal of a hard-loving wife of a narco.

"The film's climax in particular allows Gomez to shine as a dramatic actress in new ways. She conveys heartache and anguish through a tortured physicality that propels her into the unpredictable state of a woman on the verge of something dangerous."

Asked by the BBC's Graham Norton if it was comfortable going back to the world of singing and dancing for the musical, Gomez said: "No, because this was completely different.

"It was intricate dance moves I never knew my body could do, and it was also me playing a character so if anything I tried to avoid what I was comfortable with."

There has also been praise for Gascón, a "wonderful discovery" who gives "a magnificent performance", according to the Hollywood Reporter's David Rooney.

The Telegraph's Tim Robey described the film as "amazingly confident – it’s clever, earnest, ridiculous, knowing, forceful and absolutely bonkers", while Hoai-Tran Bui of Inverse said it was "an emotionally fulfilling triumph".

Not all critics were as enthusiastic about the film, however.

"Emilia Pérez was originally intended to be an opera, which perhaps partly explains its saccharine sentimentality, repetitive lyrics, and diverging story branches. But that doesn’t excuse its almost random, whiplash-inducing tonal pivots," said Slant's Kyle Turner.

However, Lauren Bradshaw of Fangirl Freakout said: "Emilia Pérez is a magnificent, genre-bending thrill ride that transcends the typical movie construct, breathing a fresh burst of excitement into the way we think about film."

As an actress, Gomez is best known for starring in Only Murders in the Building, but also has a successful singing career with hits including Back To You, Wolves and Love You Like a Love Song.

Her co-star Saldaña, meanwhile, has starred in a large number of blockbusters in the last two decades, with roles in the Avatar and Guardians of the Galaxy franchises.

It remains to be seen whether Emilia Pérez could be a big awards player, but Academy voters may see an opportunity to recognise Saldaña's box office success via this more critically acclaimed work.

Their co-star Adriana Paz is a Mexican actress whose credits include Not Forgotten, Hilda and La Caridad.

But the film's breakout star is arguably Gascón, who already had a successful acting career before transitioning in 2018.

Praising her performance in his review, Rooney said: "The warmth, the joyous self-realisation, the complexity and authenticity... that illuminate [Gascón's] characterisation no doubt owe much to the parallels in the Spanish star’s life - in her own words, she was an actor before becoming an actress, a father before becoming a mother."

Emilia Pérez has already been selected as France's entry for the best international feature category at the Oscars, which take place in March.