Elizabeth of Suffolk

See her Daughter About section for links; Isabella Plantagenet

"Having said so much of the Prince of Wales, I cannot take leave of this subject without paying a just tribute to the memory of the illustrious Spaniard, who was not only his contemporary, but singularly attached to his person, and to the English nation in general. This was Don Sancho Martinez de Leyva, son of Don John Martinez de Leyva, first lord of the bed-chamber to king Alfonso XI. and Adelantado Mayor of Castile. His son Sancho came over to England, where he offered his services to Edward III. and attended on John duke of Lancaster in his expedition to Scotland. He afterwards went into France, and served under the Prince of Wales, with whom he was at the famous battle and victory of Poitiers. After this he commanded the English army in [77] Picardy, and was very instrumental in the advantages gained over the French in those wars; and from his remarkable strength of body was called Brazo de fierro, or "Iron Arm." In recompence for his services, when he returned to England, Edward III. to testify his regard for his person, gave him in marriage his natural daughter Elizabeth, by Elizabeth Suffolk, countess of Northumberland, granting him further the privilege, in addition to his paternal coat armour, to quarter the armorial bearings of England." Dillon, 76-77.

"There are ascribed to this king [Edward III] two natural children, viz. John Baldac 4, and Isabella, married to Sancho Martinez de Leiva 5, a Spanish nobleman, who on her account quartered the English leopards in his ecutcheon." Carte, 539.

For a discussion of Sancho and the supposed relationship of his wife to Edward III, see Casa de Leiva and ill dau of King of England and Edward III's illegitimate daughter ? at soc.genealogy.medieval, visited Jan. 3, 2013.

Sources

Thomas Carte, A General History of England, Vol. 2 (London, 1750). John Talbot Dillon, The history of the reign of Peter the Cruel, king of Castile and Leon, Vol. 2 (London, 1788).