William Luca Costa-Marsden
Born on Dec. 14, 2012, William Luca Costa-Marsden is Marsden's third child, whom he shares with former girlfriend Rose Costa. The Westworld actor shared that although it had been about seven years since he was around diapers and babies, he wasn't too worried: "Once you become a father . . . it's like riding a bike — once you learn it, you sort of got it."