Figured as much. The emperor knows that she's the one he slept with, and is close to the captain, and thus knows of his feelings for her. So he's trying to get rid of him. He's not called the "tyrant" in the title for nothing.
I know it's just speculation but I'll put the following thought into a spoiler window:
I can't wait the moment she finds out the Emperor knew it was her he slept with from the first moment she saw her in the palace after the fact, it's rather obvious now