Alphonso was born at Bayonne, in Gascony, and named after his maternal uncle, King Alfonso X of Castile, who was his godfather. Alphonso died at Windsor, aged ten, shortly after the birth of his younger brother (later Edward II of England). His death left his brother as the only surviving male heir of Edward I. Alphonso was interred at Westminster Abbey.

As heir-apparent to the throne, he bore the arms of the kingdom, differenced by a label azure of three points

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