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
Frances Seymour, Duchess of Somerset thus incurred the Queen's wrath. Essex was executed on 25 February 1601 for allegedly conspiring to murder the Queen. He left behind his wife and small children; Frances was less than two years old at the time. Frances's brother was Robert Devereux, 3rd Earl of Essex, and she had an elder sister, Dorothy. She also had three younger half-siblings from her mother's third marriage in 1603 to Richard Burke, 4th Earl of Clanricarde. These were Honora, Mary and Ulick Burke, 1st Marquess of Clanricarde. On 3 March 1616, Frances married at Drayton Bassett William Seymour, 2nd Duke of Somerset (1588-1660),