It's kinda pointless to mention that a ruler is also an ambassador.
"Guillaume Chénier
Ruler of Imperskoe Viys'ko iz Fheuv'na, Duke of Iato, Ambassador of Imperskoe Viys'ko iz Fheuv'na"
I'm pompous, but that *that* pompous.
At worse, have it put as "Ruler and Ambassador of".