They meeting the king of France must have really been a great honour for the king I am so sure of it. Even after 3 years, the son still remembers the promised made about marriage concerning the eldest daughter. That's to show the love that is still strong even within.
I think the fault should come from the daughter. She didn't actually promise the man marriage from her heart but due to she was scared. That should not have been done at the first place if I should reason it from what I actually believe in