Princess Diana didn't understand why she wasn't "enough" for her husband Prince Charles

Anne Allan has now told of their painful sessions in her new memoir 'Dancing with Diana', in which she said Diana once sat in a class and told her: "I just can't seem to do anything right when it comes to my husband.

"I do love him so much and want him to be proud of me, but I don't think he feels the same way.

"I don't understand why I am not enough for him; I think he prefers an older woman ... I know he is seeing Camilla again."

Diana started taking dance lessons with Anne weeks after she married Charles at St Paul's Cathedral, London, on 29 July, 1981.

The royal's breakdown in her lesson came in 1986 and was the first time Anne heard her famous client mention Charles' future wife Camilla Parker-Bowles.

She said Diana added: "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?"

Diana was killed on 31 August, 1997 - five years after she and then-Prince Charles split, before they finalised their divorce in 1996.

Two years after Diana's death, Charles and Camilla publicly revealed their relationship.

Diana famously told of their affair in her TV interview with journalist Martin Bashir, saying: "There were three of us in this marriage, so it was a bit crowded."