A crazed fan “freaked out” Irish actor Colin Farrell on the set of his new film, “London Boulevard,” causing him to scream “like someone had shot him.”

Farrell was filming a scene for the movie in London when a female admirer snuck past security and leaped into the backseat of a car he was in.

A source said: "This woman came from nowhere and tried to jump in the car while they were shooting a scene. Colin went crazy and started screaming like someone had shot him. He was shouting at the girl to keep away. It really freaked him out."

The 33-year-old actor just wrapped filming for “London Boulevard,” co-starring Irish-English actress Anna Friel and British beauty Keira Knightley, on August 14.

The film is set for a 2010 release, and features Farrell as a criminal who develops a relationship with a reclusive actress.