Elizabeth of Rhuddlan was the eighth and youngest daughter of Edward I of England and Eleanor of Castile. Of all of her siblings, she was closest to her younger brother Edward II, as they were only two years apart in age.

Eleanor of Castile was Queen of England as the first wife of Edward I. She was educated at the Castilian court and also ruled as Countess of Ponthieu in her own right from 1279. After diplomatic efforts to secure her marriage and affirm English sovereignty over Gascony, 13-year-old Eleanor was married to Edward at the monastery of Las Huelgas, Burgos, on 1 November 1254. She is believed to have birthed a child not long after.