Princess Diana previously sat down for an interview with Andrew Morton in his book “Diana: Her True Story.” The book was released in 1992, right after the late royal’s separation from Prince Charles was announced.

The reason why Princess Diana decided to expose the truth about her marriage to Prince Charles had to do with another book that was previously written about the royal couple.

In the book “The Firm,” royal author Penny Junor said that her book, “Charles and Diana: Portrait of A Marriage,” incensed the Princess of Wales. In the book, Junor said that Princess Diana and Prince Charles’ marriage was not a happy one due to a number of reasons.

“They were leading largely separate lives with separate friends, which was sad, but that it was a successful working partnership nonetheless. They both worked hard, both made a real difference in their charitable activities, were a terrific double act for the house of Windsor and were both excellent parents,” Junor wrote.

But according to the royal author, what really incensed Prince William and Prince Harry’s mom was the suggestion that she was happy with her marriage to Prince Charles. She decided to talk to Morton to tell the whole world what her union to the future King was really like.

However, Junor also claimed that the way Princess Diana painted Prince Charles during her previous interviews was grievously unfair for the heir to the throne. In 1995, Princess Diana also said some hurtful things about her ex-husband during her interview for Panorama.

“Nothing would convince the majority of the British people that Charles was anything other than a villain who used Diana as a brood to produce the heir and spare he needed; that their marriage was a sham from the start and the woman he really loved and continued to bed throughout, was Camilla,” Junor said.

The royal author said that the claims were neat but they were not entirely true.

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