Maybe this will be another strain in the 2 princes relationship. I'm guessing the princess's change of heart would make it seem like no one really love the crown prince and yet the duke get it so much and now he feels so alone and thus he hates the duke even more. But that was just theory from my experience reading too many manga/webnovel, not a real spoiler (sorry

). I do hope that I'm wrong and the actual plot is more interesting than what I thought, that would be fun.