Camilla sent a note to Diana asking her to meet up when Charles was away in the run-up to the royal wedding. But during the lunch Diana got suspicious when Camilla pressed her on whether she would go hunting with Charles when she moved to Highgrove, royal biographer Andrew Morton claimed. Diana was confused by the question and told Camilla she would not be taking part.
The royal author added that Camilla was relieved as she saw hunting as a way to continue her relationship with Charles.
Writing in Diana: In Her Own Words, Mr Morton said: “It was during that meeting, arranged to coincide with Prince Charles’s trip to Australia and New Zealand, that Diana became suspicious.
“Camilla kept asking if Diana was going to hunt when she moved to Highgrove.
“Nonplussed by such an odd question, Diana replied in the negative. The relief on Camilla’s face was clear.
“Diana later realised that Camilla saw Charles’s love of hunting as a conduit to maintaining her own relationship with him.”
Charles and Diana announced their engagement in February 1981.
The prince had previously dated Camilla in the early 1970s, and despite her marriage to Andrew Parker Bowles their romance never fizzled out.
Diana married Charles in a fairytale ceremony five months after their engagement in July.
But they announced their split in 1992 and divorced in 1996.
Speaking in her 1995 Panorama interview, which was watched by an estimated 15 million people, Diana sensationally claimed there were “three of us” in her marriage to Charles in reference to Camilla.
And she added that it was “a bit crowded”.
A year earlier, Charles admitted his infidelity with Camilla after his marriage became “irretrievably broken down”.