Pippa Middleton in Paris, France April 14, 2012 Credit: FameFlynet

Pippa Middleton could face jail time if prosecuted in a shocking new case involving a paparazzi photo taken in Paris on Saturday.

The 27-year-old socialite and entrepreneur, sister of Duchess Kate and sister-in-law of Prince William, was in the front passenger seat of an Audi convertible in the French capital as the driver pointed a semi-automatic handgun at photographers.

A witness in the gun-waving incident charged a formal complaint with Paris police; Middleton (plus her pal, fashion mogul Arthur de Soultrait, who was in the backseat of the car) will be summoned if authorities determine there is enough evidence for prosecution.

"If the evidence points to [Pippa Middleton's] involvement, she will be prosecuted," a judicial source told Us Weekly. "Anybody involved in the illegal use of a handgun in public is liable to arrest and interrogation."

If the pistol turns out to be real, the unidentified man waving the gun faces up to seven years in prison; even if the weapon is fake, he faces two years. 

With heightened, anti-terrorist security measures currently in place in France, it is "absolutely forbidden" for anyone to use a gun to "warn people off" in the county, a police source explained to Us. "If someone has a license then for a weapon then it must be kept covered at all times, and away from members of the public." See more photos from Pippa's wild weekend.

Middleton, who became an international star almost exactly a year ago at her 30-year-old sister's royal wedding to Prince William, 29, was in Paris for Soultrait's 29th birthday bash on Friday.