Yap, it does feels like that. But actually the way they addressed the king kinda cute , it could be "paeha" or ", "cheona" (most common way to address king/emperor) also this is like a many many centuries ago, no such a thing as equal at that time, quite sad. And if you notice in earlier, jun is depicted as the kind of tyrant emperor so if myung call him that even in a private I guess it was understandable? Isn't it?
Isnt it strange to call your hubby "Your higness" even in bed?