Why Princess Diana Couldn't Use Prince Charles' Name Until They Were Engaged

There are some pretty unusual things about Prince Charles and Princess Diana's courtship, like the fact that they only went on 12 dates before getting engaged. Far from being overwhelmed by love and wanting to get married right away, royal biographer Sally Bedell Smith told People that Prince Charles "was obviously anguished, and he said she was someone I could learn to love."

Adding to the complexity of the relationship was that Prince Charles had dated Diana's older sister, Lady Sarah, for several months. Royal protocol also meant that Princess Diana and Prince Charles couldn't really get to know each other as they were dating — Princess Diana wasn't even allowed to call him by his first name.

"It was not until Lady Diana was formally engaged to His Royal Highness The Prince of Wales that she was given permission to call him 'Charles,'" wrote Andrew Morton in the biography Diana: Her True Story (via Insider). "Until then she had demurely addressed him as 'Sir.'"

Prince Charles, however, called his then-girlfriend Diana rather than by her title, Lady Diana. "In Prince Charles' circle this was considered the norm," wrote Morton.

It may have been "the norm" for England's upper-crust, but the formality was a precursor to the unhappiness Princess Diana would feel as a member of the royal family, bound by tradition and duty. In a 1995 interview with BBC1's Panorama, the royal opened up about her rocky marriage as well as the pressure she was put under by the public and the media. In the interview, Princess Diana hinted that she and Prince Charles remained distant long after he proposed.

"Well, I don't think I was allowed to have any [interests]," she said. "I think that I've always been the 18-year-old girl he got engaged to, so I don't think I've been given any credit for growth. And, my goodness, I've had to grow."