Barton’s boinking her director. Despite recently exchanging numbers with ho-hopping musician John Mayer, Mischa Barton has been secretly dating director Brett Simon (Center) for several months. The pair met on the set of Simon’s teen movie The Assassination of a High School President, which also stars Bruce Willis and Demi Moore’s daughter, Rumer.

“This is a major love affair… Mischa was pretty insecure about carrying the movie. Brett was the one who helped her get over that by spending hours alone with her helping her develop her character and define her performance,” an insider reveals to the press.

“This is the most serious Mischa has ever been about a guy and he’s the most mature man she’s ever dated. They’re in love and no matter what happens with this movie, this is going to stay serious.”