Patrick Dempsey joins 'Valentine's Day'

To play a doctor in the ensemble romantic comedy

Patrick Dempsey is not a doctor, but he plays one on TV -- and now in the movies.

Dempsey has joined the cast of New Line's romantic comedy "Valentine's Day," being directed by Garry Marshall.

The ensemble already includes Julia Roberts, Anne Hathaway, Jessica Alba, Jessica Biel, Jennifer Garner, Shirley MacLaine, Bradley Cooper, Ashton Kutcher, Topher Grace, Emma Roberts and Hector Elizondo.

"Valentine's," which begins shooting this week, follows five slightly interconnecting stories playing out in Los Angeles during Valentine's Day.

Dempsey will play a married obstetrician dating Garner's character on the sly, with her unaware of his status.

Mike Karz is producing with Wayne Rice. Sam Brown and Michael Disco are overseeing for the studio. Katherine Fugate wrote the initial draft; Abby Kohn and Marc Silverstein penned the most recent version.

Dempsey, one of the stars of ABC's "Grey's Anatomy," most recently appeared on the big screen in the 2008 romantic comedy "Made of Honor." He is repped by UTA and the Burstein Co.