Disputes arose between two family members; Prince Fernando's young son, Alfonso de la Cerda and his uncle, Prince Fernando's younger brother, Sancho de Castilla who began jockeying for power and influence to see if he would gain power over the succession of the Castilian crown.
Sancho IV was married to María de Molina who was the sister of Don Lope Diaz' wife.
Before long, the other nobles of Castile became envious of Lope's enormous power and began to take their issues up with the King.
The argument allegedly resulted in Lope pulling out a knife and threatening the life of the King where after he was executed.
e metió mano a un cuchillo e dejóse ir para la puerta donde estaba el Rey el cuchillo sacado e la mano alta... ballesteros e caballeros, veyendo que el Conde iva contra el Rey, firieron al Conde, e diéronle con una espada en la mano, e cortáronsela, e cayó luego la mano en tierra con el cuchillo; e luego diéronle con una maza en la cabeza, que cayó en tierra muerto.He married Juana Alfonso de Molina, daughter of Alfonso of Molina, niece of the King Alfonso IX of León, and sister of the wife of King Sancho IV of Castile.
The wedding took place at the Monasterio de Santa María y San Andrés and the following marriage brought two children: