Санчо IV
Soon after this incident, Juan Núñez I allied himself with Juan Alfonso de Meneses, Lord of Alburquerque against Sancho IV and the two of them persuaded the king to release his brother, the infante John of Castile who had been in prison since 1288 when he and Lope Díaz III de Haro were uncovered in a plot. Haro was assassinated by order of the king for his role in this plot. By 1291, Sancho IV and Juan Núñez I agreed that Juana Núñez de Lara, Juan Núñez I's daughter, would marry the infante Alfonso de Castilla y Molina, the son of King Sancho IV. However, the infante Alfonso died in 1291 in Valladolid at the age of 5. Due to the past agreement between Sancho IV and the Lord of Lara, James II of Aragon, the new King of Aragon and brother of Alfonso III of Aragon, desisted for the moment in his policy of support for the succession claims of Alfonso de la Cerda.