Background
He predeceased his father, unmarried and without issue at the age of about 22.
He predeceased his father, unmarried and without issue at the age of about 22.
In 1196, Theresa and Alfonso"s marriage was annulled and she and Ferdinand went to live at the court of her father in Portugal. After the death of Sancho in March 1211, Theresa came to an agreement with Alfonso IX and returned to León. With her former husband"s assistance she hoped to secure the wealth of properties that had been left to her in her father"s will against the claims of the Portuguese crown.
As a result of this agreement, Alfonso broke off his alliance with Castile.
He co-signed charters with his father and was referred to as "infante Fernando, the king"s firstborn son". Although the treaty weakened the Castilian defences on the border by forcing them to hand over four castles to the Leonese to be demolished, it probably also strengthened the position of Alfonso VIII"s grandson against the eldest son Ferdinand in a possible future succession crisis.
He did not sign any further charters during the period of peace, but on 22 April 1213, Ferdinand again co-signed a charter with his father.