Paris (CNN) -- A friend of Pippa Middleton's, the sister-in-law of Britain's Prince William, apologized Wednesday for an incident in which a friend of his brandished a toy gun at press photographers in Paris.
Arthur de Soultrait said he, Middleton and a friend of his were in a car being followed by paparazzi on Saturday when the unnamed friend waved the toy pistol at the photographers.
Middleton "had no idea he was going to do that and told him to stop immediately. She did not find it funny," de Soultrait said in a statement.
She had been "subject to constant and dangerous harassment by paparazzi throughout her time in Paris," he said.
"I regret enormously that this incident happened, and especially that Pippa has been subject to subsequent attention through no fault of her own," he concluded.
Middleton is the younger sister of William's wife, Catherine, Duchess of Cambridge. William is second in line to the British throne behind his father, Prince Charles.
Photos of Middleton in the car with the man wielding what seems to be a gun caused a storm of outrage which should act as a wake-up call, royal watchers warned.
"This story is very damaging for her," veteran London-based public relations expert Max Clifford said.
"There has been nothing but a honeymoon for Pippa since last year's royal wedding, so this is dreadful," Clifford said. "It comes particularly at a time when guns in Paris are such a sensitive issue. The reality is, she could have been shot by police."
Middleton has been a target for tabloid newspapers and paparazzi since her sister married Prince William in April 2011.
Shortly after the wedding, personal pictures of the 28-year-old began to leak out to the press, including a photo showing her in a bikini while on vacation in 2006 with her sister and Prince William.
A photo of Middleton sunbathing topless on that trip was also made public. Later, undated photos from a private party showing her dancing in her bra were leaked.
Lawyers said Middleton was unlikely to face charges over the incident in Paris unless it could be proved that she encouraged the driver to point the gun on public streets, but the driver could face charges of threatening with a firearm.
Buckingham Palace said it would not comment on the photo because Middleton is not a member of the royal family.
There has been a spate of gun violence in France recently, including a series of attacks last month that killed seven people, including three children.
The incident took place while security was heightened ahead of France's presidential election.
"Pippa must understand she's in the middle of a media spotlight, and she can't just turn the attention on and off," Clifford added. "I assume she has PR advice, but either she's getting incredibly bad advice, or she's not listening."
The photographer who snapped the shot was "considering his options" about a formal police complaint, The Sun reported.
The Daily Express' royal correspondent Richard Palmer commented that ever since Middleton became last year's most celebrated bridesmaid at the wedding of her sister, she has been "riding the crest of a wave of popularity. Some think she has also been riding for a fall."
Palmer said Middleton was popular at high-society events, but she and her friends needed "to learn how to behave in front of the cameras in return."
The incident "will have embarrassed her sister, Kate, her brother-in-law Prince William and also the queen in her Diamond Jubilee year. She needs to explain herself and apologize."