Leonor, one of the three daughters of Henry II of England, married Alfonso VIII, king of Castile, and according to the claims made by Castilian chroniclers and diplomatic records in the thirteenth century, her dowry is supposed to have been Gascony, a county that Alfonso VIII claimed in 1204 and which Alfonso X renounced in 1254. In the absence of English records from the late twelfth century relating to such an unlikely grant from the English king, historians have espoused very different views on this rather mysterious matter. Moving the debate away from the actual grant, this paper aims to draw attention to the influence that Leonor's new kingdom would consequently have on European affairs. Whether Gascony was granted by Henry as his daughter's dowry or not, Castilian claims in the thirteenth century show that the marriage between Alfonso and Leonor had very important consequences.