Edmund had been created Earl of Lancaster; after Evesham he had received the forfeited Earldom of Leicester; he had been made Earl of Derby on the extinction of the house of Ferrers.

His son, Thomas of Lancaster, was the son-in-law of Henry de Lacy, and was soon to add to these lordships the Earldom of Lincoln.

And to the weight of these great baronies was added his royal blood.

The father of Thomas had been a titular king of Sicily.
His mother was dowager queen of Navarre.

His half-sister by the mother's side was wife of the French king Philip le Bel and mother of the English queen Isabella.