quarantine 'em

"Meanwhile", an observer who saw Charles die first would consider Elizabeth to continue as Queen. On observing Elizabeth's death, they would consider the throne to have passed to her second child, Prince Andrew (I think?)

These two observers, one having observed the throne to pass to William and one having observed the throne to Andrew, would then meet up and have a relativistic royal succession crisis

One way to resolve this dispute would be to recognise an official neutral legal relativistic frame of reference, and take the observations from this frame of reference as authoritative, rather than those of any subjective observer

Another is to extend the concept I mentioned earlier where no two legal events may happen "simultaneously" to mean that no two legal events may be separated by a spacelike curve

This second solution seems less practical in a scenario where the Queen and Prince Charles might be on separate starships journeying to or from distinct distant stars at relativistic speeds

If the neutral frame of reference is Earth, the first solution is also impractical because, if you were near Elizabeth at the time she died, it would be impossible to know who was the new monarch without consulting Earth, a round trip of potentially years

So I guess what you'd do is pick the *current monarch*'s frame of reference as authoritative?

So it doesn't matter if, in your frame of reference, Charles died first. In Elizabeth's frame of reference, Charles was her successor in her forward light cone and that's what counts