There is no source anywhere saying they were sleeping together that nite, which is what you seem to infer. She was married at that time, and their affair had ended pre-Diana (while Camilla was not married). That doesn't mean they didn't still care for each other; obviously they did, she gave him the infamous cufflinks. As I stated in my reply earlier, if circumstances would have been different they should have been together from the start. But it didn't work out that way. Life is funny.
If you seriously believe Charles and Camilla were not carrying on (and I do mean sleeping together) after Camilla was married, then you really must see some swampland in Florida that I'd like to offload for a small fortune.