Gibson Born in Peekskill, New York, Gibson moved with his parents to Sydney when he was 12 years old and later studied acting at the National Institute of Dramatic Art.
Baby Lucia is the eighth child for Gibson, 53, and the second for Grigorieva, 39. Gibson has six sons and a daughter from his marriage to his wife of 30 years, Robyn. The couple filed for divorce in April.
Grigorieva has a son with her former boyfriend, actor Timothy Dalton.
In August, the singer said she and Gibson have no immediate plans for marriage.
"We don't know yet," Grigorieva said of any impending nuptials. "We haven't really talked about it."