The retired NYPD officer who mistakenly yelled, “Gun!” at a crime scene, sparking the fatal shooting of a Long Island plainclothes cop, has been forced to surrender his weapons, and his gun license has been suspended.

Ex-Emergency Service Unit Sgt. John Cafarella, 58, got to the Massapequa, LI, scene last Saturday after cops had killed a knife-wielding madman.

Taking Geoffrey Breitkopf, 40, for a perpetrator, he yelled out, prompting an MTA cop to shoot Breitkopf dead.