The baby arrived Friday in advance of a December due date.

This is the eighth child for Gibson who has six sons and a daughter with estranged wife Robyn Gibson, who filed for divorce in April after 28 years of marriage.

Grigorieva has a 12-year-old son with actor Timothy Dalton.

People.com states that the Russian-born Grigorieva has no immediate nuptial plans with her actor-director beau.

Gibson, 53, and the 39-year-old Grigorieva made their first public appearance at the Los Angeles screening of "X-Men Origins: Wolverine" earlier this year.

(Copyright 2009 by VERTEXNews/Newsroom Solutions)