James Corden was greeted by a rousing chorus of applause when he made his entrance at the premiere of One Chance.
The Gavin And Stacey star plays Britain's Got Talent winner Paul Potts in the film about the aspiring opera singer's rise to fame.
James admitted he had hoped to perform the singing parts of his role but the crew had other ideas.
The actor said: "I thought I might be able to and then I sang for our producer and he said, 'No, we're going to have to get someone else to do that.'
"Apparently there's a big leap between being able to sing and singing opera, so it became very obvious very very quickly that I wasn't able to sing Nessum Dorma quite as well as they needed me to."
The vocals were eventually provided by Potts himself, who said at the premiere: "What felt weirdest was watching his mouth open and seeing my voice come out of it."
One Chance concentrates on the early part of Potts' life as he struggles to carve out a career for himself as an opera singer in a small town where he was bullied as a child, and leads up to his first audition for Britain's Got Talent.
The film takes in the singer's relationship with his wife Julie-Ann Cooper (played by Alexander Roach) and his trip to Venice where he was told he would probably never make it as an opera singer.
James said: "I never really read the script as Paul Potts' life story because this is just one part of his journey so I just always saw the film as about a young boy from an industrial steel town in Wales dreaming of being an opera singer in a world where no one really listens to opera, and through tremendous adversity never really gives up."
Julie Walters and Colm Meaney, who play Potts' parents, were also on the red carpet in Leicester Square.
Julie said: "James was fun to work with, people often ask that about other actors and you think, 'No' but actually it was really good fun.
"He's lovely, very talented and very funny. We did have some laughs."
One Chance is released in cinemas on October 25.