When the actors were outed as a couple after New Year's in 2014, skeptics wondered what Theron and Penn had in common. As it turns out, the actors are compatible in ways Theron herself hadn't realized.
"We've been friends for 20 years. He was married, I was in a long-term relationship, our spouses—not regularly, but we were in each other's lives. I think our friendship stemmed from mutual respect—more on my end, because I really didn't have a body of work 20 years ago, but my love and passion for making films—that was our common ground," Theron, 39, explains. "And also, Sean liked to have conversations outside of just making movies. That's sometimes hard to find among friends here, and that's where our friendship really blossomed. A lot of people want to tell you the answer to solving all of Africa's problems from what they've seen on CNN. Sean is not that guy. When he started working in Haiti and I started working on the AIDS front in South Africa, we spent a lot of time talking about those worlds."
Theron, who graces the cover of Esquire's May 2015 issue, admits Penn was caught off guard by their coupling, too.
"I think that for both of us there was never a moment where we thought that this—what we have today—would ever even be a possibility. Ever, ever, ever. I think we're both finding ourselves at this moment in our lives kind of shocked. Both of us," Theron says. "Just when you think you know how things are supposed to go down, life just kicks you in the ass and guess what? You don't have a clue."
"It is nice to be in something where the friendship came first. I've never had that," says the movie star, who dated musician Stephan Jenkins from 1997 to 2001 and actor Stuart Townsend from 2001 to 2010. "There's a weight to the relationship already that I don't think you have when you just meet somebody and enter a relationship," she adds. "There's a foundation of 20 years that the two of us have shared with each other in all these different ways that is really the foundation of something that has brought a lot of beautiful things into my life. We get so stuck in wanting to predict the future that we forget the moment that we're in. And the moment that we're in is just really good. It's really good, really nice."
Penn has been married twice before, to Madonna and Robin Wright. Might he propose to Theron someday? "The marriage thing is always so strange to me. I love the possibility of anything, but I'm really enjoying myself and the everyday moment and how that coincides with my son and my life and my friends. I'm a very, very, very lucky girl. Very lucky. He's hot. He is hot," she says. "How do you say that in an interview? You're a 40-year-old woman sounding like a 16-year-old. There's something beautiful about that, but you lack the articulation of really saying what it's like when somebody walks into your life and makes you see something that you really never thought you'd be able to see. If somebody had said to me, 'This is what it will be,' I would've said, 'F--k off.' As you can see, it makes me smile."
For more from the Mad Max: Fury Road actress, pick up Esquire's May 2015 issue hits newsstands Apr. 21.