LONDON -- Princess Diana's sons implored her former butler Friday to stop revealing secrets of her private life, calling a series of gossipy tabloid articles a "cold and overt betrayal" of their late mother.

In an unusually emotional written statement, 21-year-old William said Diana would have been mortified by Paul Burrell's revelations. He said he also spoke on behalf of his 19-year-old brother, Harry.

Burrell has written a book about Diana, "A Royal Duty," which has been excerpted all week in the Daily Mirror tabloid.

In a statement issued through his publisher Penguin, Burrell said he was saddened by the princes' statement "because I know that this book is nothing more than a tribute to their mother."

"My only intention in writing this book was to defend the princess and stand in her corner," Burrell said.

Burrell has written about private letters including one in which Diana reportedly said, 10 months before her death in a Paris car crash August 1997, that she feared someone was plotting to harm her in a staged car accident.

"We cannot believe that Paul, who was entrusted with so much, could abuse his position in such a cold and overt betrayal," the princes said in the statement released by Clarence House, where they live in London with their father, Prince Charles.

"It is not only deeply painful for the two of us but also for everyone else affected and it would mortify our mother if she were alive today and, if we might say so, we feel we are more able to speak for our mother than Paul.

"We ask Paul please to bring these revelations to an end," their statement said.

Clarence House said William and Harry _ who often played with Burrell's children at Kensington Palace when they were growing up _ were willing to meet with him to discuss the matter.

Burrell, whom Diana called "my rock," was once one of the royal family's most trusted servants and still professes loyalty to them. He worked for Diana for almost 10 years, was the first friend to reach her side after the crash that killed her and sat with her body through most of the following night.

He was the only mourner from outside her immediate family to attend her burial, and the queen awarded him the Royal Victorian Medal for services to the family.

The excerpts from his book, due out next week, have included references to private correspondence and a raft of intimate details about Diana's life and her relationships with her royal in-laws.

He quoted her as writing in one letter to him, 10 months before she died in Paris, that "this particular phase in my life is the most dangerous."

She reportedly wrote that someone was planning "an accident in my car, brake failure and serious head injury in order to make the path clear for Charles to marry."

Burrell quoted a letter Diana received from Prince Philip, her father-in-law, as saying he had "never dreamed" Charles would leave her for his companion Camilla Parker Bowles.

She reportedly wrote in another letter, as her marriage ended, that she had never wanted a divorce but thought her relationship with Charles had been poisoned by "envy, jealousy and hatred" from his family and friends.

Meanwhile Friday, three photographers went on trial in France for taking pictures at the scene of the crash that killed Diana or in the chase across Paris that preceded it.

The trial stems from a criminal complaint for invasion of privacy filed by the father of Dodi Fayed, Diana's companion who died along with her and her driver.

Jacques Langevin, Christian Martinez and Fabrice Chassery had pursued Diana's Mercedes-Benz. They face up to a year in prison and a fine of $53,000. The prosecutor asked that they get suspended prison terms. A verdict is expected Nov. 28.

Photos taken at the site were confiscated and never published.

The trial hinges on a French law that says the interior of a car is a private space. The photographers took pictures of Fayed through an open door of the crumpled car, or driving away with Diana as he left a hotel.

In 2002, France's highest court dropped manslaughter charges against the photographers. An investigation concluded the driver had been drinking and was driving at high speed.