06/11/2008 AT 08:45 AM EDT
Mark Wahlberg and model Rhea Durham have been together for years – and are proud parents to daughter Ella, 4, and son Michael, 2.
Now, as the couple expects baby number three
, are they finally ready to walk down the aisle?
They haven't announced an engagement, but the actor did
call Durham his "future wife" at the New York premiere of his new film, The Happening
"I did my own thing for some 30-odd years," he told PEOPLE at the Tuesday night event. "I had a blast, and now I feel like I have a real purpose."
The actor dropped the "wife" word when discussing his 37th birthday on June 5. "I had a beautiful day with my kids and my future wife," he said. "We went to brunch."
As for the impending arrival, Wahlberg revealed that they're having a son, and that Durham, 29, is due in September. "We're thrilled!"
Is he worried about bringing a third baby into his already-hectic household? "For the most part, my kids are darlings," he said. "But at 5 a.m., it can be a little crazy."
costars certainly have no doubts about his parenting prowess.
"He's great with kids," said Zooey Deschanel, who plays his wife in the film. "Really, really good."
In fact, that's what made him perfect for the role (as a science teacher trying to survive a mysterious phenomenon). "When I see Mark Wahlberg, I see the sweet guy who likes to hold the baby," said director M. Night Shyamalan. "He brings humanity and vulnerability to the screen. In a crisis ... that's the guy you want with you."
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