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
Edward Seymour, 1st Duke of Somerset to throw off the Protector within two years and "bear rule as other kings do"; but Edward, schooled to defer to the Council, failed to co-operate. In April 1547, using Edward's support to circumvent Somerset's opposition, Thomas Seymour secretly married Henry VIII's widow Catherine Parr, whose Protestant household included the 11-year-old Lady Jane Grey and the 13-year-old Princess Elizabeth. In summer 1548, a pregnant Catherine Parr discovered Thomas Seymour embracing Princess Elizabeth. As a result, Elizabeth was removed from Catherine Parr's household and transferred to Sir Anthony Denny's. That September, Catherine Parr died in childbirth, and Thomas Seymour promptly resumed