On the King's watch, it's a Frogman's watch.
(Excuse clumsy translation, I let Google do it)
Euroman has talked to watch expert Kristian Haagen about the very special watch, which is an Omega Seamaster 300 42mm without date. "He is only allowed to wear it because he is a former frogman. It is a special frogman watch, which is made in direct collaboration with Omega. It is a secret watch that should not be trumpeted. There are no official pictures of it, and that's how the frogmen want it."
You can just spy it here.