Judd Apatow returns with his new movie This Is 40 this week, a comedy about the trials of marriage, parenthood and being middle aged and is billed as a 'sort of sequel' to 2007's Knocked Up. The director - who once again teams up with Paul Rudd - discussed the origins of the film with the Los Angeles Times.

"I wasn't thinking about making a sequel," Apatow explained, "I just wanted to do a movie about this age and this time of life, so I started making notes about it. And I was thinking about different actors and actresses who could be in it. And then in the middle of the night I just thought, 'I think I'm writing the sequel to Knocked Up, and it should be Pete and Debbie, and Maude and Iris.' Suddenly it made sense." Knocked Up was a runaway hit, scoring both critical acclaim and commercial success. Though it focused mainly on the relationship between Seth Rogen and Katherine Heigl's characters, Paul Rudd and Leslie Mann were perhaps the most believable characters. "When I'm writing and when we rehearse, Paul and I will sit with Leslie and [Paul's] wife, Julie, and we'll have the 'What is annoying you about each other?" Apatow said of writing the new film, "and a lot of that makes its way into the movie. So I see it more as a bizarre Frankenstein monster of my worst traits and Paul's worst traits, and then Leslie has to deal with that."

'This Is 40' hits theaters in the U.S. on Friday (December 21, 2012).  

Watch the trailer here