Everyone held their breath in England when Queen Elizabeth went into hospital a few weeks ago. Under common law, Prince Charles will automatically become King the moment the Queen dies. Prince William could only become King if Prince Charles chose to abdicate. That would require legislation, as happened with the Declaration of Abdication Act 1936. While there are "reports" he considers the job a very difficult one and not one that he wants, there are also "reports" that he's waited so long - he will take up the role.
I wondered what were the circumstances that the current Queen is only the second Elizabeth? I assume it is because if a monarch had sons, they took precedence over daughters. That was changed with the Succession to the Crown Act 2013 along with removing the disqualification arising from a marriage to a Roman Catholic. The history of the monarchy in Britain is so complicated, that I stopped looking.
I hadn't realize that there was controversy over her being the second Elizabeth: Rather than choose a regnal name; she chose to remain Elizabeth, "of course"; thus she was called Elizabeth II. This annoyed many Scots, as she was the first Elizabeth to rule in Scotland.
So much tradition: What number in the succession stops being important and becomes just a number? Is there a top 10 or 20 that count more than the others - Wikipedia goes to 63. I realized it would be those directly related to the Queen - the first twenty-four. Below is the top twenty - this comes from the official British monarchy website. It is https://www.royal.uk
So the succession of the Monarchy is importance to us today. This is a time when one can find out their ancestry and get a sense of their family tree. I expect the British Monarchy to stay around for a while given our intense curiosity about our own ancestors. And there are exciting times ahead with the countdown to the year-long Queen's Platinum Jubilee 2022 celebration.
Here's an elegant Christmas tree from a few years ago at the Fantasy of Trees.