He loves his horse...maybe to much.

The Dauphin or as they call him in the book The Duke of Bourbon feels as if his horse is the best horse in the world.  When the Dauphin begins bragging about his horse the Constable and Orleans agree with him and praise the Dauphin's horse themselves, when he starts comparing his horse various things like saying, "He is the prince of horses."  I believe this is when they decided that they could no longer tolerate the Dauphin's prideful boasting.  They really began mocking the Dauphin when he tried to say that he wrote a sonnet about his horse, when he starts to recite the sonnet Orleans recognizes it and says's it is about someones mistress, the Dauphin disagrees with him and says's that his sonnet was copied and also that his horse is his mistress, Orleans and the Constable then begin to mock him showing that they no true respect for the Dauphin.  If they had respect for him they would not have mocked him as they did.