A Scotland Yard investigation has been launched after a policeman believed to be guarding the home of The Duke and Duchess of Cambridge accidentally discharged a gun while sitting in an unmarked car.
Nobody was injured when the officer, who was sitting in the vehicle with another policeman, let off the shot while on duty in north Wales last week.
A Met Police spokesman said: "Shortly before 1pm on Wednesday October 24 an on-duty MPS police officer unintentionally discharged a firearm while in an unmarked police vehicle.
"The round damaged the floor of the vehicle. Another on-duty officer was in the vehicle at the time of the incident. Neither officer was injured.
"The officers were on duty in north Wales at the time."
Both the officers are attached to Specialist Operations, the Met said.
The spokesman said the Met's Directorate of Professional Standards has been informed of the incident and the officer concerned has been removed from B firearms duty pending the outcome of inquiries.
Prince William, or Flight Lieutenant Wales as he is known in his capacity as a RAF search and rescue helicopter pilot, captains Sea King helicopters from his unit's base at RAF Valley in north Wales.