I'm not Denville, obviously,
but IMO there is still a great deal of resentment in the UK towards Charles and Camilla that doesn't have much to do with watching The Crown, though it might stir up old feelings towards the couple for some.
Much of the support for Diana during her lifetime IMO came from British women of the same age who had young children as she did and some had difficult marriages which helped them identity with her. Of course men in the UK loved her as well. When you see videos of her funeral many men are seen to be as upset as their women folk.
Diana drew huge crowds for her engagements wherever she appeared in Britain. These events occurred more than in the Commonwealth, where she was also extremely popular, and far more than in the US and other countries. After Diana died in her 30s there was a feeling in the UK population of the unfairness of a life cut short while those who had done her wrong lived on. And IMO again, that has been reflected in the opinion polls (taken among UK residents) for the woman who became Charles's second wife.
I believe that many of those who watched this season of The Crown are young, that is under 30 year olds who are seeing aspects of Diana and Charles's married life for the first time, and instinctively are sympathetic to Diana. Many might be Americans, I don't know, and certainly a great many who are on Twitter and discuss this series probably are. But don't discount the huge number of British people of middle age and younger who've been watching, either.
And in case some here think I don't know what I'm talking about, I was born and brought up in England, have large numbers of friends and family who still live there.
I was also in England a lot in the 1980s and '90s, and, perhaps more to the point, I was there when Diana died, was among the crowds before and after Diana was buried and heard what British people were saying in those crowds about certain royals.
Memories often die hard, and I don't think feelings about Diana and Charles and Camilla can all be attributed to watching The Crown and to its American and foreign viewers by any means.