Charlize Theron admits she finds the idea of marrying her ''hot'' fiancé Sean Penn ''strange'' but insists she's a ''lucky girl'' to be engaged to him.

The 40-year-old actress readily admits Sean, 54, makes her heart skip a beat and she is madly in love with him but she still has reservations about the concept of marriage.

Charlize - whose mother shot dead her alcoholic father after he attacked her while drunk - told the new issue of Esquire magazine: ''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. 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. 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.''

Charlize - who has an adopted son, Jackson - says her and Sean's romance grew out of a deep respect for one another and a beautiful 20-year friendship.

Before, neither she or the actor were in a position to embark on a relationship but now they have Charlize feels lucky they shared such a great friendship first.

The 'Mad Max: Fury Road' star explained: ''We've been friends for 20 years. He was married, I was in a long-term relationship ... I think our friendship stemmed from mutual respect ... 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. 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 ... 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.''

The couple are expected to wed this summer. While the nuptials will be Charlize's first, Sean was previously married to Madonna from 1985 to 1989 and Robin Wright from 1996 to 2010.