Prince Charles had a simple but cruel trick he would play on Princess Diana to fool her into thinking he was home when he was really seeing Camilla, a royal author has claimed.
Journalist Andrew Morton revealed that the heir would circle TV shows in the Radio Times to lull his wife into believing he was planning on staying in, when he was having an affair.
The royal biography author unveiled the con as he said that he still gets a "shiver down his spine" when he thinks back to the things Diana candidly told him in a series of secret interviews.
He said: "Charles would circle a TV programme with his pen in the Radio Times for the evening to make her think he was at home, when actually a Ford Escort estate car had driven him 12 miles to meet Camilla Parker Bowles.
He added: "At the time, everybody still believed it was the perfect marriage – the handsome prince and his beautiful young bride. But nothing could have been further from the truth.
"It was explosive.
"One particular part of the tapes from 1991 which still gets the hairs standing up on the back of my neck was when she said she wanted to go to Paris for a weekend to walk along the pavement and not have anyone follow or recognise her."
When Morton published his biography Diana in 1992, it was condemned by the Archbishop of Canterbury and he faced so much criticism one MP suggested he should be banished to the Tower of London.
But he defends his writing as Diana's truth, and while he dismissed conspiracy theories surrounding her death, he adds she was "absolutely" being conspired against generally.
He said: "Diana felt powerless – a prisoner of the palace. She felt that she was living a lie. And everybody was living that lie – from the bodyguard to the butler to the gardener. It was taking a toll on people’s health.
"Members of royal staff suffered from all kinds of stomach problems due to the stress of having to lie to the princess.
"Charles broke his shoulder at Cirencester and the shortwave radios were listening for when Diana was driving down from London to see him in hospital.
"With Camilla already there, she had to scarper out the back when Diana arrived. It was a situation that put a great deal of strain on a lot of people.
"When Diana complained about the relationship and raised her suspicions, Charles’ friends would say: 'Don’t be such a silly girl, they’re just friends'."
Morton obtained his private tell-all talks with Diana vicariously through her life-long friend Dr James Colthurst.
Morton said: "As her friend, James was well aware that her marriage had failed and her husband was having an affair with Camilla. By this stage, Diana was very concerned for her safety and the safety of those around her.
"She was desperate to tell her story and she was living in paranoia. It was a very English coup.
"James would go to see Diana in her sitting room with tea and biscuits and stick a microphone on her sweater. He would turn the tape on and literally ask the questions I had prepared. It was a very hit-and-miss process."
Although "nothing could have prepared him" for the criticism that ensued from the publication of his book, Morton feels privileged to have been given the chance to help Diana tell her story.
He said: "I am still very, very honoured to have been asked to write the book, and I am proud of helping her to express her feelings and discuss her life in the way that she did.
"She was thrilled that millions of people understood her better – and that is a legacy that lives on today.
"I am still in awe of her bravery for doing what she did because, despite the tragic way her story ended, she was finally able to live her truth."
