Theobald II
Eleanor's marriage in 1254 to the future Edward I of England was not the only marriage her family planned for her. The kings of Castile had long made a tenuous claim to be paramount lords of the Kingdom of Navarre due to sworn homage from Garcia VI of Navarre in 1134. In 1253, Ferdinand III's heir, Eleanor's half-brother Alfonso X of Castile, stalled negotiations with England in hopes that she would marry Theobald II of Navarre. The marriage afforded several advantages. First, the Pyrenees kingdom also afforded passage from Castile to Gascony. Secondly, Theobald II was not yet of age, affording the opportunity to rule or potentially annex Navarre into Castile. To avoid Castilian control, Margaret of Bourbon (mother and regent to Theobald II) in August 1253 allied with James I of Aragon instead, and as part of that treaty solemnly promised that Theobald would never marry Eleanor.