Isabella Mortimer

Isabella Mortimer, Lady of Clun and Oswestry (born after 1247; died before 1 April 1292) was a noblewoman and a member of an important and powerful Welsh Marcher family. Although often overshadowed in modern historiography by her better-known parents, she is now known to have played an important part in her family's struggles against Llywelyn ap Gruffudd and to have helped to secure the frontline at Shropshire in the run-up to English conquest of Wales. She was the wife and widow of John III FitzAlan, baron of Clun and Oswestry and de jure earl of Arundel. After a lengthy widowhood, she married for a second time and largely disappeared from the records.

Isabella was born some time after 1247, possibly at Wigmore Castle, Herefordshire, the daughter of Roger Mortimer, 1st Baron Mortimer and Maud de Braose. Her father was a celebrated soldier and Marcher baron; and her mother was a staunch royalist during the Second Barons' War who devised the plan for the escape of Prince Edward, the future King Edward I of England, from the custody of Simon de Montfort, 6th Earl of Leicester. She had one sister and five brothers, including Ralph, would-be heir to the family estates, who predeceased his parents, and Edmund Mortimer, 2nd Baron Mortimer.

Before 14 May 1260, Isabella married her first husband, John III FitzAlan, the son and heir of John II FitzAlan, baron of Clun and Oswestry and de jure earl of Arundel, and Maud de Verdun. In due course John the younger would succeed to the baronies of Clun and Oswestry, but as long as the dowager countess of Arundel remained alive the FitzAlans did not possess the complete earldom or its title. Consequently, Isabella Mortimer never held the title of countess of Arundel, which remained until 1282 with Isabella de Warenne, the childless widow of Hugh d'Aubigny (d.1243).