Castilian Civil War
Fernando Sánchez de Tovar was the "Adelantado Mayor" of Pedro of Castile at the start of the First Castilian Civil War, but in 1366 he betrayed the King and delivered the city of Calahorra to Pedro's brother and enemy, Henry of Trastámara. One year later, Fernando Sánchez de Tovar fought on Henry's side in the Battle of Nájera.