The blonde socialite - the daughter of singer Rod Stewart - is expecting a child with 'The Wolfman' star, but the pair are not in a relationship.
The actor's representative Robin Baum confirmed the news to Life & Style magazine, saying: "Kimberly is pregnant. Benicio is the father and is very supportive. Although they are not a couple, they are looking forward to the arrival of the baby."
It is not known when 31-year-old Kimberly and Benicio, 44, were dating.
The new arrival will be Rod's first grandchild.
The 66-year-old musician recently welcomed his eighth child, Aiden, into the world in February, his second son with wife Penny Lancaster, 40.