Charles Seymour, 6th Duke of Somerset the pride of birth and rank amounted almost to a disease". Charles was the second son of Charles Seymour, 2nd Baron Seymour of Trowbridge (died 1665), of Marlborough Castle in Wiltshire, by his wife Elizabeth Alington (1635–1692). The 2nd baron was (in a junior line) a great-great-grandson of Edward Seymour, 1st Duke of Somerset (executed 1552), brother of Queen Jane Seymour, uncle of King Edward VI and Lord Protector of England. Charles was educated at Harrow School and Trinity College, Cambridge, where his portrait by Nathaniel Dance-Holland survives in the College's collection. In 1675, Charles's elder brother Francis Seymour, 5th
Duke of Somerset him Marquess of Hertford in 1640 and on 13 September 1660, shortly before his death on 24 October, the title of Duke of Somerset was granted to him as its legitimate heir; following its non-existence for 108 years. He outlived his three eldest sons and as the dukedom descends to heirs male of the holder of the 1547 grant it passed to William Seymour (1654–1671) who was the son of the third son mentioned (lived 1626–1654). The 3rd duke died unmarried and the title passed to John Seymour (bef. 1646–1675) the last surviving son of the 2nd Duke, his uncle.