Elizabeth II, the Queen of Great Britain, is not only an Anglican, she is the nominal head of the Church of England. One of the titles that she still bears, inherited, ironically, from Henry VIII, is "Defender of the Faith" – ironic because the title was bestowed by the pope, before they had their little falling out.
Prince Charles, the heir apparent, has said that he will change that title to "Defender of Faiths." So, will Charles be head of the Church of England when he is king? Will he defend all faiths, while keeping his own the established church of England?
The Church of England is in deep trouble. Though most English people are members, very few attend. The Anglican communion worldwide is fighting with itself. The Archbishop of Canterbury can't get the U.S. Episcopal Church to play nicely with all the other churches in the touchy worldwide organization.
Perhaps the accession of King Charles III (or George VII, or whatever he picks) will lead to the best thing that could happen to the Church of England: disestablishment. Christianity as a whole is in deep trouble in Britain, and no one thing will help much. But the Anglican Church might be free to evangelize and grow, if it were freed from the responsibility of being the praying arm of what has become a secular establishment, presiding over a diverse society.
I don't know what Charles Windsor's actual faith is. He has not been the stolid churchwoman that his mother is. He has invested his political capital in defending traditional architecture, rather than traditional religion. His sons, likewise, have not suggested that church is the core institution in their lives.
Someday, Elizabeth II will not be queen, hard though that is to imagine. Odds are that her son will succeed her. And sometime after that may come a day when the Church of England is one church among many, the British monarch is just another member of that church, or even another denomination, and the Anglican communion is a loose association of denominations – led from Nairobi.