Prince Charles and Princess Diana
Prince Charles and Princess Diana at Westminster Abbey, London, for a centenary service for the Royal College Of Music on Feb. 28, 1982.  Getty Images/Hulton Archive

Prince Charles made a “huge mistake” for failing to do something before he proposed to Princess Diana.

According to Penny Junor in her 2017 book “The Duchess: The Untold Story,” the Prince of Wales hid his past romance with Camilla Parker Bowles to Princess Diana. He told the People’s Princess that the Duchess of Cornwall was just a friend and he did hold off the truth until after his proposal.

“He came clean after the engagement,” Junor wrote.

“He had not handled things well. It didn’t occur to him that she needed to know before someone else told her.”

Prince Charles and Princess Diana’s relationship quickly changed when the latter learned that he had an affair with Camilla before her. Prince William and Prince Harry’s mom reportedly broke down. Princess Diana became moody, willful and unpredictable. She also became jealous of anyone who spent time with Prince Charles, including Queen Elizabeth II.

Camilla put some distance between her and the royal family when she learned that Princess Diana was anxious about her. She even turned down a number of invitations from Prince Charles.

Prince Charles assured Princess Diana that there would be no other woman aside from her. They pushed through their wedding despite his initial hesitation, thinking that things would be better once they got married. Unfortunately, things just got worse.

Prince Charles wasn’t really over Camilla. In fact, he broke Princess Diana’s heart with his “stupid decision” during their honeymoon by taking Camilla’s photo. In addition, he decided to wear the cufflinks that Camilla gave to him as a present. The accessory featured entwined C’s that reportedly represented the first letter of their names.

Princess Diana confronted Prince Charles about the cufflinks and asked if they were from Camilla. The heir didn’t deny and insisted that nothing was wrong because they were from a friend.

However, Princess Diana was very affected by it. According to the late Princess of Wales’ butler Paul Burrell, Princess Diana asked him to pick off all the C’s of her Chanel shoes and handbags. He added that Princess Diana “couldn’t bear” to see two entwined C’s from then on.