John de Beaufort, 1st Marquess of Somerset, 1st Marquess of Dorset, 1st Earl of Somerset, was born circa 1371 to John of Gaunt, 1st Duke of Lancaster (1340-1399) and Catherine De Roet (1350-1403) and died 16 March 1409 of unspecified causes. He married Margaret Holland (1385-1439) 28 September 1397 JL . Alfred the Great (849-899)/s, Charlemagne (747-814)/s, Henry II of England (1133-1189)/s, Hugh Capet (c940-996)/s, William I of England (1027-1087)/s, Rollo of Normandy (860-932)/s.
|Offspring of John Beaufort, 1st Earl of Somerset and Margaret Holland (1385-1439)|
|Margaret Beaufort (c1400-1449)|
|Henry Beaufort, 2nd Earl of Somerset (1401-1418)|
|John Beaufort, 1st Duke of Somerset (1404-1444)||25 March 1404||27 May 1444||Margaret Beauchamp (c1410-1482)|
|Thomas Beaufort, Earl of Perche (1405-1432)|
|Joan Beaufort (c1406-1445)||1406||15 July 1445 Dunbar, East Lothian||James I, King of Scotland (1394-1437) James I, King of Scotland (1394-1437) James Stewart (c1383-aft1451)|
|Edmund Beaufort, 2nd Duke of Somerset (1406-1455)||1406||22 May 1455||Eleanor Beauchamp (1408-1467)|