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
Mary Seymour, Duchess of Somerset in Wiltshire and Devon. On 11 September 1744, the unexpected death of George Seymour, Viscount Beauchamp (1725–1744), the only son of Algernon Seymour, 7th Duke of Somerset, made Sir Edward the heir presumptive to the dukedom and to the barony of Seymour. On 23 November 1750 the 7th duke died, and Seymour succeeded to the dukedom, his wife then becoming a duchess. The principal Percy family estates and houses of Alnwick Castle, Northumberland House, Petworth House, and Syon House, had been divided between the 7th duke's daughter Elizabeth Percy, Duchess of Northumberland, and his nephew, Charles Wyndham, 2nd Earl of