King Charles reportedly underestimated Princess Diana throughout their course of marriage.

A former butler of the couple reveals Diana felt under confident in the presence of His Majesty.

In book A Royal Duty, former butler Paul Burrell shared: "I saw the confidence-crushing effect [King] Charles had on her in Japan when she tried to win his approval."

"Charles and his staff were checking their watches as they milled in the grand hallway ahead of an official function when the princess, looking radiant, came downstairs wearing a Catherine Walker red tartan coat dress with red velvet collar and cuffs," the former butler explained.

"It was loud but elegant and she was smiling. I was waiting at the bottom of the stairs when she walked to the prince's side and said, 'So, do you like my outfit, Charles?'"

"His reply was soft and devoid of bitterness, but its effect was brutal," the ex-royal butler said. "'Yes. You look like a British Caledonian air stewardess,’” he revealed.