Mischa Barton dating movie director

Mischa Barton is dating the director of her new film, reports claim.

The former OC star has been having a secret relationship with Brett Simon for several months.

The pair met on the set of teen movie The Assassination of a High School President, which also stars Bruce Willis and daughter Rumer.

A source told the Daily Mail: "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.

"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."

Simon is known for directing a series of short films and the video for The Killers' hit 'Somebody Told Me'.

Barton was recently criticised by St Trinians co-star Antoniah Bernath for being "unprofessional" on set.