Royal fans and avid viewers of "The Crown" alike know that the marriage of Prince Charles (opens in new tab) and Princess Diana (opens in new tab) was not the fairy-tale love story that people expected, but royal expert Elizabeth Holmes takes that analysis a step further.

Elizabeth Holmes, author of HRH: So Many Thoughts on Royal Style (opens in new tab), told Us Weekly magazine (opens in new tab) that the Welsh couple's marriage "was almost like a business deal. Princess Diana met so many requirements and blended right in."

The expert then described the royal couple's extremely short courtship period. 'It was very short,' she said. It speaks volumes about how Prince Charles approached the matter and what kind of pressure he felt. ...... It was almost a formality," he said. That doesn't really sound good. [Of Princess Diana, who married at only 19, Holmes says, "She made this big life decision without a stable family and without a lot of guidance. 'In hindsight, it's very easy to spot red flags... It's as if we were saying, 'We are marching. We are doing our duty.'"

"It was like, 'We are doing our duty.'

As Holmes might have predicted had he been on the case at the time, the two, parents of Prince William (opens in new tab) and Prince Harry (opens in new tab), divorced in 1996 (opens in new tab). Princess Diana died in a car accident in Paris in 1997 (opens in new tab). Prince Charles (opens in new tab) married his longtime girlfriend Camilla Parker-Bowles (opens in new tab) in 2005.