Camilla Parker Bowles reportedly called Princess Diana a “mad cow,” among other things. She is pictured attending London Fashion Week in London on Feb. 19, 2019.  Eddie Mulholland-WPA Pool/Getty Images

They competed for Prince Charles’ affections for years, and now, an explosive new report claims that Camilla Parker-Bowles didn’t have very nice things to say about Princess Diana while she was married to the future king.

In the 2018 book “Rebel Prince: The Power, Passion and Defiance of Prince Charles,” royal biographer Tom Bower revealed that over the years, the future Duchess of Cornwall didn’t take to kindly to Princess Diana, referring to her as a “mouse” and then getting extremely angered when the royal couple’s marriage officially fell apart—and Diana called out the then known affair that Parker Bowles was having with Prince Charles at the time in an interview.

Following Diana’s famous interview where she claimed her marriage had been “crowded,” Bower claims that Camilla became enraged, referring to the princess as a “mad cow” and indicating she was guilty of several affairs of her own, meaning she couldn’t complain about Charles’ one dalliance when she had been “working her way through the lifeguards.”

The affair officially began in 1986, the two women even had a confrontation with one another in 1989 when both attended a birthday party at Annabel Goldsmith’s house and Diana allegedly told her husband’s mistress to leave him alone.

However, Bower claims that instead of choosing to “stand back to allow Charles and Diana to reconcile,” Parker Bowles “coldly pushed her rival aside.” He stated that while she acknowledged the hurt she caused the other woman after their confrontation, she remarked it was appropriate to discuss in a private home, and also privately defended herself by saying she was guilty of only having one extra-marital affair.

Bower’s claim comes after Diana’s biographer, Andrew Morton, published letters that Camilla had written to Charles in his 2004 book, where she also referred to the princess as a “ridiculous creature” before she and Charles officially separated in 1992.

Of course, while their relationship was contentious, it has been reported since that after her own marriage to Charles in 2005, Parker Bowles deferred from the title of Princess of Wales out of respect for Diana, who passed away in 1997. As a result, she became the Duchess of Cornwall, and potentially set the precedent for royal wives to receive duchy titles, like Kate Middleton and Meghan Markle, who married Princes William and Harry, but did not take on Princess titles.