"Secret" is a relative term, up until about 10 years ago I suspect very few had heard of it, I'd be interested in anything online before 2016 referring to them

"Secret" is a relative term, up until about 10 years ago I suspect very few had heard of it, I'd be interested in anything online before 2016 referring to them (there was big media coverage in 2017) The specific details however aren't public knowlege, with various secrecy levels, and there are various different plans depending on the situation (what happens if the queen was on a plane that crashed for example, or what if Charles died in an avalanche in Austria), and plans of course are constantly changing (what happens if there's a massive pandemic which means people can't congregate in their millions to pay respects as they did with Diana, what happens if the news is leaked on twitter before coordinated official announcement)