The treaty was sealed with a marriage alliance between the Angevin and Capetian dynasties. John's niece Blanche, daughter of his sister Leonora and Alfonso VIII of Castile, married Philip's eldest son, Louis VIII of France (to be eventually known as Louis the Lion).
A formal agreement was concluded by linking the Angevin and Capetian royal houses through a familial bond, specifically in the union of John's niece Blanche with Philip's eldest child Louis, who would eventually become famous as Louis the Lion.