Am I allowed to usurp a title from my liege?

I am playing as the Duke of Bohemia. My liege is the Kaiser. My vassals have 2 of the 3 counties of the (de jure) Duchy of Moravia.

I was planning to create the title Duke of Moravia, but the Kaiser (my liege) created the title for himself first.

It looks like I can usurp the Duke of Moravia title once I have enough money. Is that true? Also, could the Kaiser usurp the title back from me?

EDIT: Upon closer examination, I discovered that my brother (who held the 3rd county of de jure Moravia) had the Duke title. (I assume he was given the title by his liege the Kaiser, although I don't remember seeing a notification.) I was able to usurp the Duke of Moravia title from my brother.

Solution 1:

No, you can't usurp a title from your liege.

You can usurp a title from your sibling-vassals and anyone from another kingdom, though. It will be possible to usurp that title if you declare independence and win (because you can't usurp a title from anyone who's at war). Since the Holy Roman Empire occasionally enters bouts of multiple rebellion, maybe you can join the crowd and earn your freedom the next time it comes around, then usurp the duchy afterward.

(Note: I haven't tried to usurp a title from a liege, but it's telling that none of my vassals have ever tried to usurp one from me. I've even held a duchy when a single vassal owned all of the counties in that duchy — I eventually passed that duchy onto someone else so I wouldn't have to deal with the "vassal wants the duchy" penalty. My vassals usurp titles from each other from time to time, so they're plenty capable of it.)