Cameron Diaz said she "barely worked out" before her role in The Other Woman alongside Sports Illustrated model Kate Upton.
The 41-year-old actress, who is seen running down a beach in a bikini with Kate, 21, in the new movie, admits she wasn't worried about her figure and being filmed with an actress half her age.
"When I did that scene I was barely working out. I wasn't like 'Oh my God, I am going to be in a bikini and Kate is going to be in a bikini and what is everyone going to think of me,' she told 2Day FM radio station.
"I am 20 years older than her. I am not trying to be her. She is a beautiful woman. We are completely different and I celebrate her."
Asked if she wished she could be 21 again, she said: "I am very happy to be 41 and I love it.
In the movie, Diaz plays a lawyer named Carly who is having an affair with good-looking cad Mark, played by Nikolaj Coster-Waldau.
When wife Kate (Leslie Mann) finds out, instead of directing her anger at Carly, the pair team up and recruit yet another “other woman”, Amber (Kate Upton) to wreak their revenge.
Speaking about the concept of the movie, she said: “The idea that women have to hate each other and fight over a man is really outdated.
"We used this story of betrayal, in the way of adultery, as a way to bring together three women who would have never otherwise come together.”