As with nearly all kings in history, King Afonso IV of Portugal was used to getting his own way no matter what the situation. It just seems to be a king, with all that power, seems to have a negative effect on their minds, no? So when he was not happy with his son choice of a wife, Ines, he forbade the marriage.
The reason being that Ines was apparently illegitimate. Meaning she may have already been married or was not of nobility. His son, however, Don Pedro, in his own princely fashion decided he would not listen to his father and kept seeing Ines. In fact, their relationship continued to the day they announced they were actually married.
As you can imagine King Afonso was not so happy about not being listened too. Even if Don Pedro was his heir, this could not do at all. He decided he would end their relationship once and for all, exiling Ines to a monastery where she was confined. It just sounds like a fairy tale, doesn’t it?
But when it comes to real life, that happy ending is so far and seldom to materialize. As in 1355, Afonso decided he was done playing these games with his son and sent three henchmen to murder Ines. Don Pedro was devastated and possibly pushed a bit into the realm of madness. How could he seek his revenge? Well he couldn’t his father was the king, so he waited for his father to die. And two years later, he became king himself.
Don Pedro aka Peter I Of Portugal, first order was to rip the heart’s of his wife’s murderers right out. Yet he never actually caught the third murderer, and maybe this lack of being able to seek his complete vengeance is what drove him over the edge. Because later during his reign, he had Ines corpse exhumed and had her crowned. Pedro would sit on the throne next to his dead queen Ines and make all the nobility file passed. They even had to kiss her bony hand to show loyalty!