Mel Gibson and Oksana Grigorieva
05/25/2009 AT 07:00 PM EDT
Six weeks after his wife Robyn filed for divorce after 28 years of marriage, Mel Gibson has some news of his own: his Russian musician girlfriend Oksana Grigorieva, 39, is pregnant, the actor's rep confirms exclusively to PEOPLE.
"He couldn't be happier," says a Gibson friend. "He loves being a father."
Grigorieva, who is signed to Gibson's record label, Icon Records, is in her second trimester and due in the late fall.
For those eager to point to Grigorieva's pregnancy as a catalyst for Gibson's divorce
, they'll be wrong, says the close source: "This has nothing to do with the divorce. Mel didn't even know Oksana was pregnant when they filed."
Gibson's wife Robyn, who cited "irreconcilable differences" in her April 13 divorce petition, has remained mum on his relationship with Grigorieva and the pregnancy rumors. According to Gibson's own divorce response, filed on the same day as Robyn's, he and his wife separated almost three years ago.
Gibson, 53, who has seven children with Robyn, including their youngest, 10-year-old son Thomas, and Oksana, who has a son, Alexander, with her former boyfriend, actor Timothy Dalton, stepped out
for the first time at an industry screening for X-Men Origins: Wolverine
in L.A. on April 29.
Grigorieva's son and the Gibson kids have met and vacationed together and, says a source, get along well.
The baby news is not expected to complicate legal matters, experts say.
"This pregnancy won't have any effect on Mel Gibson's pending divorce," says L.A. family lawyer Michael Trope, who's not involved with the case. "Just having a girlfriend alone is only relevant if Mel spent large sums of community money on her during his marriage."
Without any indication the ex-couple had a prenup, Robyn is legally entitled to half of Gibson's fortune, estimated at close to $1 billion.
Because of this, experts agree this divorce won't be messy and will probably resolve quietly in several months.