The movie is a family affair for the Apatow clan. Not only does his wife of 15 years play the lead, but their two daughters, Maude (13) and Iris (8), play the unbearably spoilt children who make up the onscreen family unit.
"There's all this sibling rivalry in our house, which was always really difficult for Leslie and me to watch because we love our kids but they fight all the time," he says. "And it was odd, but by making this movie the two sisters bonded and they've been much closer as a result of portraying their mutual hostilities on film," he laughs.
Clearly, the comedy giant, whose material is largely gleaned from personal experience, has no problem shining a spotlight on his home life, regardless of it being largely unflattering.
"Comedy is best when it shows people at their worst. A more well-adjusted family than this one wouldn't be as fun to watch, so you show the difficult moments.
"As far as relationships, I wanted to show that when you're married for a long time, the mystery disappears.
"It's hard to keep up the romance and I wanted to give one or two examples of how that happens. I have never asked Leslie to inspect my anus," he says, referring to a particularly sensitive scene, "but I do many gross thing during the day. When you're around someone for that many years, at some point you stop closing the door when you got to the bathroom.
"But there's nothing in this movie I'm embarrassed about. Some people are shy about certain things, which I understand, but in my work I like there to be no limitations."
Apatow vividly recalls his own experience of entering his fourth decade. "The day I turned 40, I visited Leslie on the set of Seventeen Again, where she was dancing with Zac Efron," he smiles, shaking his head. "It went on for many hours, spinning and twirling." He sighs.
"That's what my day was like, watching this young boy with chiselled abs erotically hold my wife. Eventually I left the set and cried while I waited for her in her trailer."
Who: Judd Apatow
What: This is 40
When: Opens today
- TimeOut