Prince Charles was indicating that he didn’t love Diana in so many words. Of course the prince knew what love is. He felt it for his family, I would assume. He certainly felt in love with Camilla, so Charles was stating that he was doing his duty and marrying the sacrificial lamb to make his family (mum and dad) happy.
Diana fit. Young. Young enough to still be a virgin. Blue blood. Good background. She ticked off all the boxes for what Prince Charles needed in a wife and future Queen. The only problem was they were too different. Charles needed someone who understood him, who stood behind him, giving him the chance to shine at event and walkabouts. Diana didn’t fit this at all. She tried! Diana was shy, got over it, enjoyed the adulation of the people, and Charles’ jealousy grew, rather than enjoying how much his subjects loved his new wife.
Diana had to have been embarrassed by her fiancé’s remark. She said she loved him, even though they hadn’t spent much time together, and I think Diana did feel euphoric about Prince Charles choosing her. She had to have felt incredibly special. Charles, on the other had, probably didn’t know what to feel. The one woman who “got” him, was married with children, and then he had dated and dallied with other ladies, but none seemed suitable to be the future Queen.
It all came down to perspective. Prince Charles knew damn well what love was. He said, “Whatever love is.”, because his “love” for Diana wasn’t there yet. They did love each other for a time. But at their engagement? They hardly knew one another. And Charles was almost saying, Help! And he might have been signaling to Camilla that he still loved her. I don’t think we’ll ever really know. But Prince Charles did still love Camilla.