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Dapper in a dark suit, Mel Gibson could have been any other churchgoer at the Holy Family Chapel in Agoura Hills, Calif., on May 24. He shook hands and laughed with other members of the congregation, enjoyed a bounty of homemade baked goods after mass and stayed close by his family, including his daughter Hannah and his two young grandchildren. But when it came to one important church activity, he abstained. "He didn't take communion," said a fellow parishioner at the traditionalist Catholic church Gibson started building in 2003. "He just stayed towards the back of the church."

Few people in Hollywood take their faith more seriously than Gibson. But he may have had good reason for not taking part. The next day his rep confirmed to PEOPLE that Gibson's girlfriend, Russian musician Oksana Grigorieva, 39, is pregnant in her second trimester with what will be the newest member of Gibson's brood. The announcement came six weeks after Robyn, Gibson's wife of 29 years and the mother of his seven children, filed for divorce on April 13. Gibson, 53, who has said that he and Robyn have been separated for three years, is excited about the baby news. "He couldn't be happier," says a friend. "He loves being a father." As Gibson told Jay Leno on May 25, "This is true; we're going to have a child. I guess I'm Octo-Mel!"

All joking aside, was the pregnancy the catalyst for the collapse of Gibson's marriage? Not according to people close to Gibson and Grigorieva. "Mel didn't even know Oksana was pregnant when they filed [for divorce]," says Gibson's friend. Grigorieva, who is signed to Gibson's record label, was first photographed with him in 2008 on the set of his movie Edge of Darkness; they stepped out publicly for the first time at a screening of X-Men Origins: Wolverine in Los Angeles on April 28. Grigorieva's mother, Lyudmila Chernukha, a retired music teacher who lives outside Moscow, bristles at any suggestion her daughter played a role in the divorce. "He split up with his wife three years ago, so to suggest that she has broken up their marriage is rubbish," Chernukha told PEOPLE. "He was no longer with his wife, so he was bound to meet some woman at some point—it just happened to be Oksana."

Gibson's marriage had indeed been troubled for a long time. "These things happen. It's unfortunate. It's sad. But you know she is an admirable woman—we still got kids to raise together. We're friends," Gibson told Leno. "When it's all said and done, I did a pretty good hatchet job on my marriage myself. I'm to blame." Friends say the pair's ongoing personality conflicts were exacerbated by Mel's public struggle with alcohol. (Gibson has said they separated in August 2006, less than a month after his notorious drunk driving arrest in Malibu.) "The tension between Mel and Robyn was obvious," says a close family friend. "During family dinners, they wouldn't speak sometimes. Robyn would pretend that everything was perfect, but no one would ever dare to ask her how she and Mel were doing."

While Gibson's wealth is estimated at nearly $1 billion, legal experts say Grigorieva's pregnancy should have little effect on what promises to be a record-setting divorce settlement. "Just having a girlfriend alone is only relevant if Mel spent large sums of community money on her during his marriage," says L.A. family lawyer Michael Trope, who's not involved with the case. Without any indication the ex-couple had a prenuptial agreement, Robyn is legally entitled to half of Gibson's fortune, and experts expect the divorce to be settled quietly in the next few months.

For now Gibson and Grigorieva have been keeping a low profile in Malibu, dining at a local Russian restaurant and meeting up at Gibson's office or home after Grigorieva finishes her days in the recording studio and her 11-year-old son, Alexander (from a previous relationship with actor Timothy Dalton), gets out of school. "It seemed very important to Oksana that Mel and her son bond," says a source. "Mel is fun to be around and great with kids." Oksana and Alexander have spent quality time with Gibson and his children. When Gibson is out solo, he has a new spring in his step. "For a while when he used to come in here, it seemed he had lost the spark, but the spark is back again now," said an employee at the PC Greens grocery store after Gibson stopped in for salsa and guacamole on May 3. "Mel seemed very energized and full of life." On May 24, as Gibson visited a favorite haunt, the restaurant Nobu, a photographer asked him how he was feeling. His answer? "Groovy."