This illustration from a fourteenth centry French manuscript depicts the beheading of Pedro of Castile. The image appears in the Grandes Chroniques de France (Bib. Nat. Fr., FR 2813 fol. 447).

Edward III fought alongside Pedro at the Battle of Najera, and Pedro's daughter Constance married John of Gaunt.

If you are so inclined, you can also take a look at the banner (bearing the Castilian coat of arms) that Pedro used.