The star's wife Jamie gave birth to son Julian Ryder on 11 January (13) at the Good Samaritan Hospital in Los Angeles, his representative tells People.com.
The new arrival, who weighed seven pounds, eight ounces (3.4 kilograms), joins big sister Kylie.
A statement from the proud parents reads, ""We were curious to see how our 3-year-old would react to her new little brother, and it turns out that she couldn't be more in love.
""So far our biggest problem is that she wants to hold him all the time. It's really beautiful to watch.""