Well, you know there are ranks and posts in any army. So in my theory Kion's rank is general or I would say the General of the Army (it's the highest rank in the army of my country same as in yours) or General Field Marshal (now its not so popular in the world). And his post is the Head Commander, the Head of The Headquarters and the Defense Minister in one while the King/Queen is the Supreme Commander. Here in Ukraine we mostly call all types of generals (Major General, Lieutenant General and others) just generals when it is not some official event. What's more he's still the Prince, Queen's advisor and second in line until Kiara's son (in my theory she had a son) is born.