According to RadarOnline.com, his girlfriend Oksana Grigorieva, 39, has given birth to a baby girl.
The baby, who was due in December, arrived Friday, the celebrity Web site reports. The baby and Grigorieva are doing fine and reportedly are already home.
Gibson, 53, has seven children with his estranged wife Robyn, who filed for divorce in April, and Grigorieva has a son, Alexander, with her former boyfriend, actor Timothy Dalton.
"I have a 12-year-old, so I've been a mother for 12 years - and of course, there is no first-time mother's trepidation as such," Grigorieva said on a British TV show in September.
Speaking of her relationship with Gibson, she said, "Actually we have no plans to marry whatsoever. I haven't thought about it - we haven't spoken about it."