They're at odds with one another, though, at the beginning of the new film, from director Nick Cassavetes ("The Notebook").
Diaz plays a lawyer in a relationship with a man ("Game of Thrones" star Nikolaj Coster-Waldau) who turns out to secretly have a wife (Mann). Eventually, Diaz and the wife team up with the husband's other mistress (Upton) to get the ultimate revenge on the two-timer.
On the London red carpet earlier this month, the three leads revealed that they have all bonded off-camera.
"We really became very close friends," Mann said when asked about her real-life relationship with Diaz and Upton.
"They're such great women," Diaz said of her two co-stars.
"When I first started modeling, I didn't really have anybody that helped me find my path, gave me advice, and I thought that would be the same in acting, but it's not." the budding actress said. "Leslie and Cameron are people that I know I can call whenever I need help."
Watch the video above to see the stars at the film's U.K. premiere.
"The Other Woman" opens in theaters on Friday.