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

Princess Diana referred to Prince Charles as “sir” during the early days of their relationship.

Royal biographer Andrew Morton shared the information during his interview on ITV’s “The Royal Wives of Windsor.” He also said that he cannot imagine Meghan Markle ever calling Prince Harry “sir.”

Morton, who recently released the book “Meghan: A Hollywood Princess,” also dished on Princess Diana and Prince Charles’ romance. He said that Prince Charles, who was 30 at that time, didn’t want to settle down with Princess Diana, 19.

“At the age of 30, Charles was showing no signs of settling down. On paper, Diana was absolutely perfect as a royal bride. All of these things seemed to be important at this time,” he said (via Express).

Morton was referring to the fact that Princess Diana was a virgin when she tied the knot with Prince Charles. She also came from an aristocratic family.

However, even though Princess Diana was considered a good catch, her marriage to Prince Charles can be described as a tumultuous one.

“Everyone was acting in what they perceived to be the best interests of the institutions but it was doomed. But it was not a fairytale, it was a nightmare. I think it shows that there has been a breakdown in the class system when a royal marries a commoner,” Morton explained.

Other than talking about Princess Diana, Morton also opened up about Markle during a separate interview. While promoting his book, he told CTV News correspondent Paul Workman what he really thought of Prince Harry’s fiancée.

“You know what surprised me the most about Meghan? It was the activism in her early life. She was organizing demonstrations about the Gulf War in her schoolyard when she was aged 10. Many of her friends thought she was going to be a lawyer or a diplomat, or a politician,” he said.

But Workman claimed that Markle settled for being a princess. But this is not necessarily a bad thing. Markle is the type of princess that stood up to the mean girls in school, and she also volunteered at a soup kitchen on Skid Row in Los Angeles.