Charlize Theron and Sean Penn are now one of Hollywood's most high-profile couples, but their romance was 20 years in the making. In a new interview with Esquire, Theron, 39, reveals how her relationship with the actor came to be.

“We’ve been friends for 20 years," the Mad Max: Fury Road star begins. "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 goes on to explain how an emotional relationship was the foundation for what ended up turning romantic.

"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," she notes. "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."

Related: Sean and Charlize Step Out Amid Engagement Rumors

She continues, "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. 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."

The 54-year-old actor and Theron have been seeing each other for over a year, and clearly they knew it was more than just a fun fling from the start.

Related: Charlize Theron on Clashing With 'Mad Max' Co-Star Tom Hardy

"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 says. "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."

Naturally, the actress didn't elaborate on if "that moment" means they are currently engaged and played coy regarding marriage plans.

Related: Sean Penn Would Consider Marrying Again

"The marriage thing is always so strange to me anyway. 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," she tells the mag. Penn is in the process of formally adopting her 3-year-old son Jackson.

For his part, Sean — who has been hitched to Madonna (1985-1989) and House of Cards star Robin Wright (1996-2010) — is equally as smitten. He told Esquire U.K. earlier this year that he'd consider it a "first marriage" not third, if he walked down the aisle again with his "love" Charlize.

"I’m a very, very, very lucky girl. Very lucky. He’s hot. He is hot. How do you say that in an interview? You’re a 40-year-old woman sounding like a 16-year-old," Charlize laughs. "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."

Read more from Theron's interview in the May issue of Esquire on newsstands April 21.