WATCH: What were the royals thinking by inviting Camilla to Charles and Diana's wedding?
Every bride remembers her wedding day. For some, it may have been the best day of their lives. But for the late Princess of Wales, it was a bitter-sweet moment.
According to royal biographer Sally Bedell Smith, Princess Diana was "distracted" while walking down the aisle to greet her future husband Charles. In the congregation, she spotted her fiance's then ex-girlfriend Camilla Parker-Bowles.
Their fairytale wedding was broadcast around the globe on July 29, 1981. To the world, Diana looked like the blushing bride, but inside she had to contend with being the "other woman".
Speaking on this week's episode of CNN documentary series 'The Windsors', Bedell Smith explained that Diana found herself competing with Camilla, even on that most "magical" of days.
"As Diana walks down the aisle with her father, she sees Camilla," the US author and historian says in a clip shared exclusively with the Daily Mail's FEMAIL.
"There she is, on this magical day, and the one thing she is focusing on is the image of Camilla."
The documentary concentrates on how Charles was forced to choose a bride out of a sense of duty. "Charles persuaded himself that he could be in love with Diana," royal biographer Tina Brown explained in the episode. "At least enough in love to get married."
It also touches on Britain's obsession with the royal couple and their romance, unaware of the turmoil that was going on behind the scenes.
"[They were] totally in love with this ideal couple," Dr Edward Owens, author of 'The Family Firm', added in the documentary. "And yet, the public can't see everything."