"They just drifted apart," says a close friend of the couple of the amicable split. "They're both working hard on their careers and trying to raise a sweet baby together. They're still friends and they'll both raise [their daughter] together."
The two welcomed daughter Lucia on Oct. 30, 2009.
Gibson has seven children with his estranged wife, Robyn, who filed for divorce from the actor in April 2009 after nearly three years of separation. Grigorieva also has a son from a previous relationship with ex-boyfriend Timothy Dalton.