It was meant to be the happiest day of his life, but as Prince Charles made his way out of St Paul's Cathedral with his new wife Princess Diana, he met the gaze of Camilla Parker-Bowles – the woman he never stopped loving. In the crowd his ex-girlfriend looked downcast and wearing an expression that matched the greyness of her suit.

According to royal author Penny Junor, the prince's highly publicised day was tinged with sadness and he had a "slightly plaintive look" on his face as he looked at his one-time lover. "Their wonderful affair was over, and reality was kicking in," Junor writes.

This is one of the many explosive revelations about the famous royal love triangle in the tome The Duchess: The Untold Story – which is being serialised by the Daily Mail.

The late Princess of Wales would later recall that very moment in secret tapes she sent to biographer Andrew Morton. "As I walked up the aisle, I looked for her [Camilla]. I knew she was there of course."

She added: "Walking back down the aisle, I spotted her... To this day, you know – vivid memory."

Before exchanging vows in front of millions, Charles and Diana had had a blazing row over a gold bracelet he has gifted his Camilla with the initials of the nicknames they had for each other, 'Gladys' and 'Fred'. Despite Charles' insistence that was no other woman in his life, a jealous Diana had resented the intimate gesture.

"What enraged Diana most of all was a bracelet destined for Camilla that she found on Michael Colborne's desk one Friday afternoon," Junor said of couple's toxic relationship. "Diana confessed she'd had a look at what was on his desk but said nothing further about it."

"She became jealous — obsessing about Camilla and turning against people she'd appeared to like, convinced they were out to get her, undermine her or spy on her."

Charles rekindled his romance with Camilla following the collapse of her marriage to Andrew and Diana's death. The pair tied the knot in a civil ceremony in 2005.

Prince Charles and Diana
Princess of Wales with Prince Charles of Wales at their wedding at St Paul Cathedral in London in this file photo dated 29 July 1981. Getty