Before Diana and Charles wed in 1981, the monarch and Camilla, 77, dated in the ‘70s, before parting ways. Camilla went on to marry Andrew Parker Bowles in 1973, before later divorcing in 1995. However she allegedly went on to have an affair with Charles in 1986, a subject which caused Diana a great deal of pain.

“‘I know he is seeing Camilla again. Am I expected to accept that, like the other Princesses of Wales before, one just turns a blind eye to husbands having a mistress!’” Allan wrote, recalling Diana’s emotional admission to her.

“‘Why does he not love me? I really don’t understand. I have tried everything, tried to conform to his wishes even though I don’t always agree. There’s no affection between us, and I am always on my own. I just want to be loved. I can’t keep going on like this. They are really expecting me to just say nothing and keep going. How do I do that?’”

In 1992, after a number of years of marital strife, Charles and Diana decided to separate and formally divorced four years later. Yet even despite the divorce, Diana was determined to make sure Prince William and Prince Harry were at the heart of her decisions as she vowed to keep her family “together”

She tragically died one year after her divorce was finalised.