Heiress Presumptive
On the death of Alfonso VIII in 1214, the crown passed to his heir prince Henry (third and sole surviving son of the late king), who was only ten years old. Thus began a period of regency, first under the young king's mother, lasting 24 days until her own death, and then under his sister and heir presumptive Berengaria.
At this point internal strife began, instigated by the nobility, primarily the House of Lara. This forced Berengaria to cede guardianship of the king and the regency of the realm to Count Álvaro Núñez de Lara in order to avoid civil conflict in Castile.
In February, 1216, an extraordinary parliamentary session was held in Valladolid, attended by such Castilian magnates as Lope Díaz II de Haro, Gonzalo Rodríguez Girón, Álvaro Díaz de Cameros, Alfonso Téllez de Meneses and others, who agreed, with the support of Berengaria, to make common cause against Álvaro Núñez de Lara. At the end of May the situation in Castile had grown perilous for Berengaria, so she decided to take refuge in the castle of Autillo de Campos, which was held by Gonzalo Rodríguez Girón (one of her allies) and sent her son Ferdinand to the court of León and his father, Alfonso IX. On 15 August 1216 an assembly of all the magnates of Castile was held to attempt to reach an accord that would prevent civil war, but disagreements led the families of Girón, Téllez de Meneses, and Haro to break definitively with Álvaro de Lara.
Read more about this topic: Berengaria Of Castile