Prince Charles and Camilla Parker-Bowles celebrated their 15th wedding anniversary last April at their Birkhall residence in Aberdeenshire, Scotland. 

The heir to the throne and the Duchess of Cornwall, whose romance has spanned decades, tied the knot in 2005 in a civil ceremony at the Windsor Guildhall followed by a dedication in St George's Chapel at Windsor Castle. 

Prior to their wedding, however, the couple had a complicated and controversial relationship. 

Camilla was portrayed as the "third person" in Prince Charles and Princess Diana's marriage and was accused of the downfall of their relationship. 

Furthermore, while she is now considered as one of the senior members of the royal family, she still had a difficult time setting up her royal charities because of the late People's Princess. 

Camilla Struggled Not To Overshadow Princess Diana

In a Channel 5 documentary Charles and Camilla: King and Queen, a royal expert explained that the Duchess of Cornwall struggled to build her own organization as several charities were linked with Princess Diana. 

"All senior members of the Royal Family have their favorite charities. The charities that they support, the issue they're most passionate about. In Camilla's case, it was very difficult for her because so many causes that we understand she actually did care about were associated with Diana," Journalist Daisy McAndrew said in the documentary. 

This left Camilla having to tread "carefully" and not to look like she was trying to replace Prince Charles' former wife. 

"She had to be so careful not to tread on Diana's image or Diana's favorite subjects or charities.," McAndrew furthered.

Moreover, the journalist pointed out that it would not have been a wise decision for Camilla to aim at any of Diana's previous foundations during her marriage with the heir to the throne. 

"It would, of course, look like she was trying to walk in Diana's shoes. That was a very difficult line to tread."

The Duchess of Cornwall currently serves as a patron to numerous literacy charities, including the Wicked Young Writer's Awards and Beanstalk, the National Literacy Trust, Book Trust and First Story. 

Prince Charles' Devastation Over Camilla's Previous Marriage

Before rekindling their relationship following the Prince of Wales' messy relationship with Princess Diana, it was also reported that Prince Charles underwent severe emotional turmoil when he found out that Camilla was engaged to then-husband Andrew Parker-Bowles in 1973. 

In the same documentary, royal expert Katie Nicholl revealed that Prince Charles was in the West Indies and felt "crushed" when he heard the news about Camilla. 

"One can only imagine that Charles would have been feeling pretty crushed by this news. He had gone away to serve and hoped that Camilla would wait for him. He certainly thought the relationship had legs, even if his family didn't," Nicholl said, referring to Charles being away with Camilla for several months. 

READ MORE: Kardashian Scare: Kendall Jenner Reveals MASSIVE Impact Of COVID-19