[quote=@FistOfZeus]
I mean obviously this is dependent on the player of the princess, but a possible reason for the dislike relates to Hawke's usage of "black magic". The princess rules over the sorcerers and sorceresses, presumably the most powerful magic users in the land, and a desire to annex them under his control to gain access to those magics works as a basic initial reason for his interest. From there interpersonal issues between the two can be expanded upon by the players. Maybe he proposed in such a way that was more command than question and she took offense, maybe he gave her an ultimatum, I dunno. Just tossing a few ideas around.
[/quote]
I had considered that. I had other ideas as well. It really depends on the personality and background story for the princess, but this is some of the other ideas that I was throwing around as well: 

[list]
[*]Hawke doesn't actually dislike the princess at all, but must publicly pretend to. This would be in order to keep up appearances and allow him to conquer her nation with more ease. Perhaps Tethe'alla's people are pushing for annexation or there is a more political reason (ex: problem with trade, the princess' nation has control over most ports on the continent, another kingdom/nation could be trying to puppet a war, etc). 


[*]Hawke is envious of the princess. He struggled to learn magic (which I plan to elaborate upon in the Roleplay itself) thanks to his bland lineage and is jealous that the princess would likely learn it naturally (considering she hails from sorcerers and such). If the princess' family is still alive, perhaps he is jealous that she was surrounded by family or has family to rely on, etc. Envy is an easy motivation and could be implemented however if needed.
[/list]
Just some ideas to name a few.