He’s called his royal attendant or advisor or something along those lines.
In the UK we also have Queen Mothers. When a King dies and it passes on to the eldest heir (used to be eldest male, but they’ve corrected that one). The surviving Queen is still treated as a Queen, but termed the Queen Mother.
I did read somewhere a long time ago that it made for an interesting introduction from the Palace operator if either of them called the other:
“Your Majesty, Her Majesty, Your Magesty”
Lord. As in Gaylord
They’re both kings.
Baron or Duke?