Actress ASHLEY OLSEN is reportedly dating NATIONAL TREASURE star JUSTIN BARTHA - after they were spotted enjoying a night out together in Las Vegas.

Bartha is currently on location in Sin City, where he is believed to be filming new movie The Hangover.

Ash, 22, flew to the city earlier this week and was photographed attending a performance of musical Jersey Boys with Bartha on Tuesday, before they headed off for an intimate dinner together.

A source tells FoxNews.com, "(They) couldn't keep their hands off each other and there was barely a break in their conversation.

"It's pretty serious. Ashley is really comfortable with Justin. It's a good fit."