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
Algernon Seymour, 7th Duke of Somerset and granddaughter of Thomas Thynne, 1st Viscount Weymouth. This Thomas Thynne was the first cousin of "Tom of ten thousand", who had been the second husband of Algernon's own mother, Elizabeth. Somerset and Frances had two children: Algernon died in 1750 and was buried in the Northumberland Vault, within Westminster Abbey. He was one of the richest landowners in England, but as he died with no surviving son his estates were split after his death. The ducal title passed to a distant cousin, Edward Seymour, 8th Duke of Somerset. The earldom of Northumberland and most of the traditional Percy estates