Felix matures very quickly due to Ember rebels assassinating the Gaul ambassador, which in turn threatens the life of his father who he has never seen or spoken to in the years of his imprisonment. And yet, Felix does his best to save him by giving up on his pride and self-perceived dignity, opening his eyes to the injustice of his and all Gaul territories' status, and simply acknowledging that he is not the center of the world, making him far less self-absorbed. He agrees to the political marriage in order to save his father from execution and takes on the vacated role of Gaul ambassador to the Ember nation.

Idealistic and clearly naive. But at least there's Growth(.gif).