Expectations were low when Paul Potts took to the stage in the auditions for the first season of Simon Cowell's TV talent contest, Britain's Got Talent. In line with our cynical, looks-obsessed times, the pudgy and timid Carphone Warehouse salesman was immediately pegged as a loser.
"He was the first of those guys where we're sat at home with our dinners on our laps going, 'Oh, here we go. This will be funny'," comedian James Corden recalls.
However, from the moment Potts opened his mouth and started to sing Nessun Dorma, the aria from Giacomo Puccini's Turandot, all bets were off. Within a few bars, the tenor had stolen the hearts of the nation with his passion and soaring voice, while a YouTube clip of his performance ensured the rest of the world quickly caught up.
The internet footage was all that Corden knew about Britain's Got Talent's first winner when Hollywood producer Harvey Weinstein - who'd seen the London-born actor-writer on Broadway the previous evening in One Man, Two Guvnors - asked him to take on the role of Potts.
Corden admits he was initially dubious about the project. "I said, 'Really? Are you sure? This sounds like a terrible idea'," he recalls. But Weinstein encouraged him to meet the director, David Frankel, who told Corden that One Chance wouldn't be about Potts' 2007 victory, but all that the singer had overcome up to that point.
In this Hollywood-inflected retelling, Potts would be a boy "from a steel town who dreams of becoming an opera singer. That two-minute YouTube clip is moving and powerful and uplifting and positive", Corden recalls Frankel telling him. "Now imagine you have seen everything it took that guy to step on the stage, how much greater that moment would be."
Convinced that what was being proposed was a Rocky Balboa-like underdog story, where opera replaced boxing, Corden signed on.
Although it purports to tell Potts' real story, One Chance at times plays loose with the facts: the film makes its protagonist a son of Port Talbot, Wales - he was born and bred in Bristol, and moved there later - and simplifies, elides and distorts elements of his life. Also, when Potts discussed the project with the filmmakers, he withheld information about the sexual abuse he'd endured as a Sea Cadet.
Perhaps this was because, as he said to the man who would portray him in the film, he hoped the movie would have some laughs in it, and that despite his many vicissitudes, it wouldn't turn into a tale of woe. "And he was absolutely right," Corden says. "He was married. He had a house. He had a job. He's already three-up on a large proportion of the world."
Film-wise, the result is a feel-good comedy drama pitted with bitter-sweet moments, and a realistic love story between Potts and his down-to-earth future wife, Jules (Alexandra Roach).
While Corden mimes to Potts' singing in One Chance, he says he didn't have to try to impersonate him. "I'm playing the Paul Potts that we never knew," the actor says. "That made it much easier, because I could bring a sense to him that I feel you need in the film. Not to say he doesn't have those things and those qualities, but I feel like there is an artistic licence you can have in the way it's done."
Something that the screen and real-life versions do share though is a shortage of confidence, the legacy of years of bullying. "I lack a little bit of confidence myself," Corden says; when he was young, he was also bullied about his size.
Instead of running away like Potts, however, he got jokes in about himself before anyone else had a chance. "It's harder to push someone over if they're right in the middle of the spotlight as opposed to the kid who's sat in the corner in the dark," he says.
The Englishman will need all the confidence he can muster if his negotiations to take over from Craig Ferguson as host of the popular American chat show, The Late Late Show, are successful. Meanwhile, he has completed work on the big-screen adaptation of Stephen Sondheim's musical Into the Woods, alongside Johnny Depp and Meryl Streep - another job that he believes wouldn't have happened if the film's director and producer hadn't seen him in One Man, Two Guvnors.
"That was such a gift of a role," he says, smiling. "It wasn't that it played to my strengths, it ignored my weaknesses."
One Chance opens on Thursday