Princess Diana and Prince Charles weren’t regarded as equals, especially before they tied the knot. While they were still boyfriend and girlfriend, the Princess of Wales could only refer to the heir to the throne in one way.

Instead of calling Prince Charles by his first name, the late royal addressed him as “Sir.” According to royal author Andrew Morton, it was only after the parents of Prince William and Prince Harry got married that Princess Diana was allowed to call her husband “Charles.”

In the documentary “The Royal Wives Of Windsor,” Morton also talked about the former couple’s marriage. He said that Princess Diana seemed liked the perfect bride for Prince Charles because she was a virgin, and she was also very young. The couple dated when Princess Diana was just 19 years old and Prince Charles was 31 years old.

Princess Diana was also an ideal wife for Prince Charles because she could give him children, and that’s exactly what she did. She gave Prince Charles an heir and a “spare.”

“Everyone was acting in what they perceived to be the best interests of the institutions but it was doomed,” Morton said. “It was not a fairytale, it was a nightmare,” he added.

But while the institution was insistent in pushing through with Prince Charles and Princess Diana’s wedding, the royal couple themselves had some hesitations. In the book “Charles: The Misunderstood Prince,” royal author Sally Bedell-Smith said that the future king wept at the window on the day of his nuptials.

“Charles lingered at a window, watching the well-wishers, and found himself weeping,” she said. “‘Stephen,’ he asked his valet, ‘Is it possible to love two women at the same time?’” she added.

Prince Charles was still in love with Camilla Parker Bowles when he married Princess Diana. In fact, if Camilla didn’t marry Andrew Parker Bowles, Prince Charles might not have gotten into a relationship with Princess Diana.

So while Prince Charles was dating Princess Diana, he was already having an affair with Camilla. Their secret relationship continued throughout the Prince and Princess of Wales’ marriage.

Prince Charles and Princess Diana Prince Charles and Princess Diana on their last official trip together - a visit to the Republic of Korea (South Korea). Photo by Tim Graham/Getty Images