Miley Cyrus' boyfriend was involved in a car accident last week.

Patrick Schwarzenegger, who is the son of actor Arnold Schwarzenegger and ex-wife Maria Shriver, was reportedly driving in the San Fernando Valley area of Los Angeles when an another driver came up and threw a full bottle of water at him before fleeing the scene.

A law enforcement source said the 21-year-old University of Southern California student allegedly started chasing the other car because he was angry.

But the insider told gossip website TMZ.com that at some point the other driver performed a U-turn and ended up ramming into Patrick's vehicle, causing minor damage.

The culprit then fled the scene again.

Patrick called the police to report the incident after meeting up with Miley, 22, for lunch at a nearby restaurant and officers have now launched an assault with a deadly weapon investigation.

The couple started dating in October after being introduced by mutual friends and insiders previously claimed Maria was worried the 'Wrecking Ball' hitmaker would be a bad influence on her son.

But a friend recently said: ''He knows what he signed up for dating Miley. She wouldn't like him if he didn't accept her for who she is and he is totally OK with what she does to express herself.

''He is with her on everything she does, as long as she doesn't get hurt he is totally down with everything.''