You could, in a way. If the King were a Duke and a Lord, you could then have someone swear to them directly, and call themself an Imperial Knight.
Indeed. If you want to swear fealty to a ruler that's also the duke of the capital, you can swear fealty to my character in Fheuv'n.
![Wink ;)](https://forum.battlemaster.org/Smileys/default/wink.gif)