“There is something you need to understand about the role I play here. One of my many duties is to determine potential advantages and potential threats to Her Highness. If you prove yourself useful to Lady Edelgard, then all will be well. If you pose a threat...I shall have to dispose of you.”
Hubert has been a stalwart servant to Edelgard and expresses undying loyalty to her. He is protective of her, and will do whatever it takes to eliminate obstacles for her, as his supports with Byleth in particular have him openly considering killing them if he thinks that they aren't useful to Edelgard.
While considered a calculating individual, Edelgard has vouched that he is honorable.