In an interview released as part of the documentary special Diana: In Her Own Words, the late Princess recounted the agonising moment her fears were confirmed.
After weeks of missed hints – like her soon-to-be husband spending time at the Parker-Bowles country home “quite a lot” and Camilla’s seemingly intimate knowledge of their plans – Diana learned the truth when she happened upon a bracelet Charles had designed for his mistress.
“I was still too immature to understand all the messages coming my way. And then someone in his office told me that my husband has had a bracelet made for her,” she explained to her close friend, who recorded the interview on behalf of reporter Andrew Morton.
“I walked into this man’s office one day and I said, ‘Ooh, what’s in that parcel?’ And he said ‘Oh, you shouldn’t look at that’.
“So I opened it and there was the bracelet. I was devastated, and I said, ‘Well, he’s going to give it to her tonight’.
Diana said she confronted Charles over the bracelet, asking him, “Why can’t you be honest with me?”
She said from his response, it was clear he didn’t care.
"But no, absolutely cut me dead. It was as if he’d made his decision and if it wasn’t going to work it wasn’t going to work."
Diana said at that moment she seriously considered breaking off her engagement, but her sisters talked her out of it.