What if Philip Mountbatten hadn’t surrendered his Greek titles, everyone before him in the line of succession died or abdicated, and then he became king of Greece, while his wife was Queen Of UK?
(Probably easiest to do this in the 1950s, less people need to die/abdicate that way)
And then, when his parents die Prince Charles becomes king of Greece and the UK, in personal Union.
How would this play out?