Even though Princess Diana was the woman who many royal courtiers approved of as a suitable wife to Prince Charles, it didn't do anything to make their marriage survive. 

From the beginning, it was known that their marriage was doomed from the start. Even the head of the monarchy, Queen Elizabeth II, thinks so. 

There are a ton of reasons why Prince Charles and Princess Diana's marriage didn't last. 

From their mismatched personalities to his lack of love for her, to cheating on her for another person. 

One of the most overlooked reason, however, is also the most significant. 

According to royal author Robert Johnson, Queen Elizabeth had a theory as to why his son's marriage to Lady Diana Spencer failed. 

In an Express UK article, Johnson said, "The queen thinks that one of the reasons Charles' marriage to Diana didn't last was because he waited too long. At 32, he was too set in his ways."

By the time the Prince of Wales announced his engagement to Lady Di in 1981, he was already facing high pressure to find a suitable spouse to share his royal duties. 

Prince Charles' elders didn't mind when he dated around and had fun during his 20s. They even turned a blind eye when he started hooking up with Camilla Parker Bowles, the woman who played a significant role in Princess Diana and Prince Charles' failed marriage. 

The elders didn't want him to marry Camilla. 

After just going on 12 dates, Prince Charles and Lady Diana didn't know each other that well, and that's when he proposed. 

Their age gap was also massive. At that time, Prince Charles was 32, and Lady Diana Spencer was 20 years old. 

But their divorce years later didn't just stem from one reason. It actually led to a lot of contributing factors. 

However, even if they were at the same age when they wed, Prince Charles and Lady Diana's marriage would still fail. 

That's because their characters were also not well-suited to each other. 

Prince Charles was raised to have a stiff upper lip and to have reserved emotions. His spouse, Princess Diana, on the other hand, was wearing her heart on her sleeve.

She didn't like how her husband didn't stick up to her or comfort her when she was being scrutinized intensely by the British media. 

The difference between Camilla Parker Bowles and Princess Diana is that the Prince of Wales' current wife is more easygoing and well-suited to him. 

Even when he was still married to the People's Princess, Prince Charles remained in contact with Camilla.

In a leaked telephone conversation between him and Camilla, Prince Charles can be heard saying, "Oh God. I'll just live inside your trousers or something. It would be much easier."

Camilla responded, "What are you going to turn into, a pair of knickers?"

The scandal was said to have been recorded in the late 80s and was leaked in 1993. 

After Prince Charles and Princess Diana separated in 1995, he and Camilla immediately started dating but didn't make their relationship public until years later. A year later, Princess Diana died.

In 2005, Prince Charles and Camilla Parker Bowles finally married.

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