Marriage and issue
Arms of Beaufort family, Earls and Dukes of Somerset: The Royal Arms of England (Quarterly, 1st & 4th: Azure, three fleurs de lis or (France); 2nd & 3rd: Gules, three lions passant guardant in pale or (England)) all within a bordure compony argent and azure[39] for difference
At some time after 1421, Thomas de Courtenay married Lady Margaret Beaufort, daughter of John Beaufort, 1st Earl of Somerset (the first of the four illegitimate children of John of Gaunt (son of King Edward III of England) by his mistress, Katherine Swynford, later his wife) by his wife, Lady Margaret Holland. Margaret was thus sister of Henry Beaufort, 2nd Earl of Somerset, of John Beaufort, 1st Duke of Somerset, of Thomas Beaufort, Count of Perche, of Joan Beaufort, Queen of Scotland, and of Edmund Beaufort, 2nd Duke of Somerset. Thomas and Margaret had three sons and six daughters:[40]
Thomas Courtenay, 6th/14th Earl of Devon (1432 – 3 April 1461), was taken prisoner at the Battle of Towton, and beheaded at York on 3 April 1461, when the earldom was forfeited.[41]
Sir Henry Courtenay (d. 1467/9[42]), Esquire, of West Coker, Somerset, beheaded for treason in the market place at Salisbury, Wiltshire on 17 January 1469 (or 4 March 1467[41]). As the earldom had been forfeited following the execution of his elder brother in 1461, he is not generally considered to have inherited from him the title "Earl of Devon", although for example Debrett's Peerage, 1968, gives him as the 7th Earl and successor to his brother.[43]
John Courtenay, 7th/15th Earl of Devon (1435 – 3 May 1471), was restored to the earldom in 1470 by the Lancastrians in exile, and later slain at the Battle of Tewkesbury on 4 May 1471.[44]
Joan Courtenay (born c. 1441), who married firstly, Sir Roger Clifford, second son of Thomas Clifford, 8th Baron de Clifford, who was beheaded after the Battle of Bosworth in 1485. She married secondly, Sir William Knyvet of Buckenham, Norfolk.[44]
Elizabeth Courtenay (born c. 1449), who married, before March 1490, Sir Hugh Conway.[44]
Anne Courtenay.
Eleanor Courtenay.
Maud Courtenay.
Agnes Courtenay (1452 – 7 January 1485), who married Richard Saunders (1452-1480) of Charlwood, Surrey.[42]