Diaz, Mann and Upton great friends
The trio star in comedy The Other Woman, about a woman who discovers her boyfriend is married, only for both her and his wife to find out he has another girlfriend. Together they set out for revenge.
The Counsellor star Cameron said: "Our objective here was to show that women don't have to be at each other's throats. We created such an absurd situation, but these women wouldn't have known each other if it hadn't been for that situation.
"It doesn't matter that these women are so different, they all know what it is to be in pain and want to help one another through that."
She added that it hadn't been hard to bond with her co-stars: "They're pretty likeable. They're cool girls."
Model Kate celebrated her 21st birthday while making the film and said: "It was the best way to celebrate my birthday, it was in the Hamptons and they threw me a party after and then on set it was our dancing scene. We knocked it all out."
Cameron agreed: "We had a 12-hour dance party."
Knocked Up actress Leslie explained how important her female friendships were outside of work, too.
She said: "I've had the same best friends since middle school and I love them so much. We do these hotel days where we rent a hotel and start as early as they'll let us in at like 10, 11 in the morning and we talk and talk and talk until like one in the morning, and drink a lot of wine and bring astrology books. We get everything off of our chests and I love it. I don't know what I would do without that day with my girlfriends."
The Other Woman is released in cinemas on April 23.