The turbulent clashes between the nobility and the monarchy at the end of the Middle Ages, witnessed episodes in which personal relationships, in particular those between men and women, could have an impact on the course of events. A good example occurred in the kingdom of Castile, where king Alfonso XI had a stable relationship with Leonor de Guzman, a woman of the high nobility of Andalucia, which resulted in a dynastic change. Following three observations proposed by Jose Manuel Perez-Prendes in his study on the myth of Frine, I will look into the case of the relationship of the king and his concubine. I will consider the role of love in the relationship, the laws that should have applied to them, and the punishment of Leonor de Guzman, who, it was alleged had separated the king from his wife, queen Maria de Portugal. It was also alleged that when the king died, Leonor was plotting to put one of her ten illegitimate children by the king on the throne, and avoid that the legitimate heir, Pedro I, could be the king.