UPDATE: 10/7/10 12:15 PM PSTVariety is now reporting that Mark Duplass, who starred in Lynn Shelton's Humpday, has joined the cast of the movie as well.

The site reports that he will play a man who comes between the sisters played by Emily Blunt and Rachel Weisz.

Original Story: Though Emily Blunt and Rachel Weisz are two of our busiest working actors, they've found time in-between their shooting schedules to appear together in Lynn Shelton's upcoming, untitled comedy project. According to Deadline, the two brunette British thespians will play sisters in the movie.

Lynn Shelton wrote the script for this untitled comedy, but like Larry David's Curb Your Enthusiasm, a lot of the dialogue will be improvised. There are no plot details at this time. The movie will be shoot on the quick, with a schedule set to last only a couple of weeks. Lynn Shelton also shot her last feature, the critically acclaimed Humpday, in a similar fashion.

Production is set to begin soon in Seattle. Steven Schardt, who served as a co-producer on Humpday, will produce.