Why Princess Diana felt "oppressed" during her honeymoon with Prince Charles.

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After they wed in a lavish ceremony at St Paul’s Cathedral in July 1981 – a seemingly fairytale wedding that was watched by 750 million people around the world – Princess Diana and Prince Charles began their honeymoon at Balmoral, the Queen’s extensive estate in Scotland.

But despite the smiles of the newlyweds and the romantic photos the world saw, royal experts say that Diana was already beginning to feel unhappy in her marriage to Charles, the Express reports.

Women We Love: Princess Diana. Looking back at the achievements and inspiration of Princess Di.

In the Netflix documentary The Story of Diana, royal photographer Jane Fincher remembers how in love the royal couple seemed during their photocall at Balmoral.

“The particular moment I remember when they looked very, very romantic – he was sort of, completely smitten by her – was when they were walking in the heather by the river,” she recalled.

“They just looked so in love and he was gazing at her, he kept picking up her hand and kissing it, just like a Prince Charming would.

“She kept putting her head on his shoulder and it was all very romantic.”

But in fact, according to historian Sally Bedell Smith, Diana felt "oppressed" during her honeymoon.

“She seemed to be having a great time, but in fact, she couldn’t stand being at Balmoral," Smith said. “She felt oppressed and hemmed in.”

“The formality of Balmoral’s intractable routine made Diana desperate," Tina Brown, author of 2007 biography The Diana Chronicles, explained.

It was also during her honeymoon that Diana "began to obsess about Camilla", added Bedell Smith.

"All she did was worry about her and whether Charles was really telling her the truth."

Although it’s believed Charles and Camilla Parker Bowles had cooled their affair right before the wedding, Diana had always been suspicious of their relationship.

After all, Camilla was a guest at their wedding, and a face that Diana specifically searched for amongst the 2500-strong crowd as she made her way down the aisle towards Charles.

“I knew she was in there, of course. I looked for her,” Diana told royal biographer Andrew Morton in 1991, as reported by Good Housekeeping.

“So walking down the aisle, I spotted Camilla, pale grey, veiled pillbox hat, saw it all, her son Tom standing on a chair. To this day, you know - vivid memory.”