In a brief update on Judd Apatow‘s next film, one that may or may not be titled This Is Forty, RopeofSilicon has noted that an addition has been made to the impressive cast. Already made up of Paul Rudd, Leslie Mann, Megan Fox, Albert Brooks, Charlyne Yi, Chris O’Dowd, Lena Dunham, Melissa McCarthy, and Ryan Lee, it’s added another actor to its roster, and that person happens to be John Lithgow.

This is a choice that some may find unusual, but he’s had an extensive career in comedy, and there’s a reason for it: The guy is, well, hilarious. I’d even say that he’s underused, having most recently gotten people’s attention in the serious role of a serial killer on Dexter. It’s good to see him get work, but even better when it’s in this kind of movie, so it’s a welcome change for him (at least when it comes to his recent projects).

I have no idea how he’ll be used here, although his somewhat theatrical but oddly naturalistic style should fit in with this kind of movie very well. That is, the kind of film I assume this will be, based off of me seeing pretty much every other movie Apatow‘s been involved with in the past several years. I like to think that gives me some room to make a guess or two on what this will be like.

The plot of the movie still isn’t known in very great detail, but we do know that Rudd and Mann are reprising their Knocked Up characters of Pete and Debbie (obviously), Brooks is Pete’s father, and Fox is said to be playing some kind of temptress to Rudd. It’s also been reported that Lee is the son of McCarthy, the latter being a schoolmate of the children of the main characters; Dunham and O’Dowd are employees of a record company, and Yi is reprising her role from the original film. That isn’t a lot to go on, but such is the nature of this thing, and I like it that way. After all, comedy is very reliant on the element of surprise, so not knowing too much about the plot or characters beforehand should be a good thing for when you actually get to see the thing. Am I alone in feeling this way? I can’t imagine that’s the case.

The film, which I’m just now going to assume is called This Is Forty, will be opening on December 21st, 2012.

How do you feel about Lithgow’s casting? Are you a fan of his comedic work?