British royal Catherine, Duchess Of Cambridge's sister is facing the possibility of arrest after a pal waved a gun at a photographer in France.

Pippa Middleton, who served as bridesmaid at her sibling's wedding to Prince William last April (11), was a passenger in a friend's car in Paris on Saturday (14Apr12), and the driver of the vehicle was caught on camera brandishing a weapon.

The Paris Judicial Police is said to be preparing to launch an investigation following the incident - and Middleton may be called in for questioning.

A source tells Britain's The Sun, "If the evidence points to her involvement, she will be prosecuted. Anybody involved in the illegal use of a handgun in public is liable to arrest and interrogation."

It is unknown if the gun was a fake firearm, but if it is found to be real, brandishing it in a public place is punishable by up to seven years' jail "for all parties involved". If the gun is a fake, the maximum prison term is two years.