In extracts from Andrew Morton's royal re-published blockbuster Diana My True Story, her brave move is revealed with transcripts of tapes recorded between the pair.
In the tapes Diana explains how she decided to confront Camilla at a birthday party attended by 40 people thrown by socialite Lady Annabel Goldsmith. Diana sprang into action after she realized her husband was once again cheating on her.
She cornered Prince Charles and Camilla at the party after they had gone to a private area downstairs with another man before requesting to talk with Camilla alone.
I said to Camilla: 'Would you like to sit down?' So we sat down, and I was utterly terrified of her, and I said: 'Camilla, I would just like you to know that I know exactly what is going on.'
She said: 'I don't know what you're talking about!' And I said: 'I know what's going on between you and Charles, and I just want you to know that.'
Camilla repied: 'Oh, it's not a cloak-and-dagger situation.'
I said: 'I think it is.'
She said to me: 'You've got everything you ever wanted. You've got all the men in the world falling in love with you, and you've got two beautiful children. What more could you want?'
So I said: 'I want my husband.' Another party-goer then came downstairs and separated the two women before Diana told Camilla, 'Don't treat me like an idiot.'
After the party, an emotional Diana confronted Prince Charles in their car about his affair with Camilla and how she had spoken to her about it at the party.
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