Charles and Camilla Parker Bowles' leaked late night telephone chat gave Diana a boost as she began rebuilding her life after separating publicly from the heir to the throne, according to her former personal protection officer Ken Wharfe.
Diana's reaction to the 1989 recording - transcribed and widely published by newspapers in 1993 - is revealed by the ex-Met Police officer in his new book Guarding Diana: Protecting The Princess Around The World.
Mr Wharfe also claims in the book the Princess was upset when Charles refused to join her at India's iconic Taj Mahal where she was photographed alone, illustrating the rift in their marriage.
Writing in the book, he quotes Diana: “'Game, set and match,' she said, clutching to her a copy of the Daily Mirror containing a transcript of the 'Camillagate' tape as we talked in her sitting room at Kensington Palace.
“Later, however, she told me that she had been genuinely shocked by some of the baser comments, particular the Prince's tampon reference. 'It's just sick,' she said repeatedly.”
The recording of the telephone call, said to have been made by a radio enthusiast using a hi-tech scanning device, featured Charles allegedly telling Camilla he would like to “live inside your trousers”.
When the then Mrs Parker Bowles, who married the prince in 2005 and is now the Duchess of Cornwall, joked “what are you going to turn into, a pair of knickers?” the heir to the throne later replied “Or, God forbid, a Tampax. Just my luck,” according to reports at the time.
The transcript had been published by national newspapers in January 1993, just over a month after the Prince and Princess formally separated and during a period when Diana was attempting to establish herself as a national figure in her own right.
Commenting on the reaction to Charles, following the publication of the tape's transcript, the former personal protection officer said in the book: “The backlash was savage. Establishment figures normally loyal to future King and country were appalled, and some questioned the Prince's suitability to rule.”
He went on to say: “Cartoonists lampooned him in the press. One cartoon, featuring him talking dirty to his plants, particularly amused the Princess, who collapsed into fits of giggles on seeing it.”
The previous year, a picture of a forlorn-looking Diana sitting in front of the Taj Mahal mausoleum - Mughal emperor Shah Jahan's monument of love to his favourite wife, Mumtaz Mahal - prompted rumours about the state of her marriage during a tour of India.
Charles was committed to his own separate itinerary at the time and was in New Delhi, where he delivered the major speech of the tour.
But Mr Wharfe, who guarded Diana for more than five years until 1993, writing in his book, said: “The Princess, who told me she was genuinely upset by her husband's refusal to join her at the Taj Mahal, had privately decided to drive home the point.”
He added when a TV journalist asked about her thoughts on the monument she turned to him for help and he advised: “Just say it is a healing experience,” and she replied to the broadcaster “It was a fascinating experience - very healing.”
The Princess gave newspapers license to interpret the remark as a comment about her marriage when, asked what she meant, she replied “Work it out for yourself,” Mr Wharfe suggested.
During the same tour, another defining image of the couple was taken, dubbed “the kiss that missed”, when Diana turned her face away just as Charles went to kiss her during a polo trophy presentation in Jaipur.
Mr Wharfe said Diana “intentionally humiliated” Charles and later when he asked her why she had done it, the Princess replied: “'Ken, I am not about to pander to him. Why the bloody hell should I? If he wants to make a fool out of me with that woman, he deserves it.”
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