Cameron Diaz: Life at 21 Was "Horrible," but Being 41 Is "Fantastic" ~ Entertainment News, Celebrity News, Celebrity Gossip

Here's another reason to love Cameron Diaz —the movie superstar has truly embraced growing older!

"I love being in my 40s," the 41-year-old bombshell told me at the L.A. premiere of her new comedy The Other Woman (in theaters tomorrow). "You know yourself and you don't give a s--t anymore. You really don't care what other people think. You let go of that things that don't matter…It's a liberation. It's fantastic."

Thinking back to her 20s, Diaz laughed, "Who wants to be 21 again? That was horrible! It was horrible! It was not the best years of my life. The best years of my life are right now."

Preach!

VIDEO: Bobby Cannavale talks about his "big" song and dance number with Cameron in Annie—watch now!

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"We concentrate too much on what's happening on the outside," Diaz said. "If you take care of what's going on in the inside, then you should have no problems."

Diaz's mid-life security wasn't the only things we learned about her at the premiere. First, she said that she hasn't used antiperspirant in about 20 years followed by the big reveal that she's been cheated on. (The Other Woman is about a housewife (Leslie Mann ) who seeks revenge on her cheating husband (Game of Thrones' Nikolaj Coster-Waldau) by teaming up with two of his mistresses (Diaz and Kate Upton ).

"Everybody's been betrayed in some way," she said. "We all have. Whether it's from a family member or a friend or a boyfriend or girlfriend. We all know what betrayal feels like."

But, she added, she has no plans to date "anyone who cheats on me again."

PHOTOS: Check some of Cameron's wackier quotes