Al Pacino has admitted he felt such terrible such stage fright singing in front of thousands in his new film Danny Collins, he forgot the words to the song.
The 75-year-old actor makes a rare comedic turn in the film about an ageing rock star who decides to change his life when he discovers a 40-year-old letter sent to him by John Lennon.
Pacino joked at the premiere of the movie at London's Ham Yard Hotel: " I'm sorry about the singing, I had to do it for the part."
But The Godfather star and Oscar winner admitted he got very nervous singing in front of such a big crowd.
Pacino said: "I'll tell you the one thing you learn about singing in front of an audience, is it's really hard to hold onto the words. You forget them because you're so nervous.
"I went on stage in the Greek Theatre in LA to perform with the great band Chicago. They had prepped the audience up for my going on and I came out as Danny Collins, and I'm so glad I was playing him, because if I would have come out myself I would have fainted dead away!"
He added: "That crowd just lifts you up, it was so exciting to do that. That was the joy of the film for me that one night."
Pacino was joined on the red carpet by British folk musician Steve Tilston, who really did receive a letter from The Beatles star 40 years after it was sent, and whose experience inspired the movie.
The film sees Pacino's character abandon a life of touring and wild parties to try to build a relationship with his family, and start writing songs again.
Pacino recalled he once crossed paths with Lennon in New York and the memory had stayed with him.
He revealed: "I ran into John Lennon. We were like ships in the night, we passed each other. But he looked at me and smiled, and we both waved. It was a moment that I'll never forget."
The funny and lighthearted film is very different to the intense dramatic roles Pacino is known for.
He said: "One of the greatest actors I know is Tom Hanks, who's an amazing actor. This is my sort of homage to Tom Hanks. I think he'd be great in the part. It's my Tom Hanks movie, I call it."
The 75-year-old star already has several more films in the pipeline, and is considering a return to the London stage, but he admitted he is having to take it a little easier as he gets older.
Pacino chuckled: "I have to slow down, between you and I, and my doctor!"
Danny Collins also stars Christopher Plummer as the rock star's manager, as well as Annette Bening, Jennifer Garner and Bobby Cannavale.
The film, which features music by Lennon, opens in UK cinemas on May 29.