Prince Charles and Princess Diana
Prince Charles used to undermine Princess Diana in the public, her private secretary revealed. Pictured: Princess Diana and Prince Charles at Westminster Abbey, London, for a centenary service for the Royal College Of Music on Feb. 28, 1982. Getty Images/Fox Photos

Prince Charles reportedly used to undermine Princess Diana even when they were in public.

In Tina Brown’s 2007 book “The Diana Chronicles,” the biographer revealed how the Prince and Princess of Wales broke down and how Prince Charles started to treat Princess Diana badly even in front of dignitaries. Princess Diana’s private secretary, Patrick Jephson, apparently told Brown that Prince Charles would begin to stick to Princess Diana during office hours.

“The Prince chose his most effective, most demoralising weapon: intellectual superiority,” the biographer said.

In 1989, Prince Charles reportedly “deliberately excluded” Princess Diana from a conversation with their royal hosts. One of the emirs eventually turned to Princess Diana and asked what she planned to do herself during the official visit.

“Diana, brightening, was about to answer with a list of the earnest programme of visits planned for her – but before she could reply her husband blithely stepped all over her,” Brown continued.

“‘Shopping, isn’t it, darling?’ he asked,” Prince Charles reportedly responded mockingly.

Jephson revealed how the future king’s words dropped into the marble stillness like bricks into plate glass. And Prince Charles did not stop there as he reportedly did it again in 1991.

During the couple’s trip to Brazil, Prince Charles shafted Princess Diana once more. On the plane out, Princess Diana referred to the briefings she was reading during their flight as her "homework." Prince Charles suddenly cut her down and said that Princess Diana didn’t know a thing about Brazil, pointing out the need for her to read those briefings.

According to Princess Diana’s former royal butler, Paul Burrell, the heir was not always kind to his first wife. Burrell even described Prince Charles as "quite cruel" to Princess Diana.

There was a time when Prince Charles likened Princess Diana to a member of the mafia due to her dress. He also reportedly once compared Princess Diana to a British-Caledonian stewardess. Burrell added that although Prince Charles was cruel, he did not stoop to physical violence.

Burrell also revealed that Princess Diana told him months before her tragic accident that she feared for her life. Princess Diana reportedly suspected Prince Charles of plotting a mobile accident to kill her so he could marry Camilla Parker Bowles.