William Seymour, 2nd Duke of Somerset was the great-grandson of Edward Seymour, 1st Duke of Somerset (c.1500-1552), the uncle of King Edward VI and Lord Protector of England. Seymour made a secret marriage at Greenwich on 22 June 1610 to Arbella Stuart (d.1615), daughter of Charles Stuart, 1st Earl of Lennox and Elizabeth Cavendish. Arbella was thirteen years his senior, and King James I disapproved of the marriage as the union of two potential Tudor pretenders to the throne, who were respectively fourth and sixth in line, could only be seen as a threat to the ruling dynasty. As a result, William was condemned to life
Duke of Somerset On his death without issue on 29 April 1675 only the Marquessate of Hertford became extinct. His distant cousin Francis Seymour, 3rd Baron Seymour of Trowbridge (1658–1678) became 5th Duke of Somerset. Francis was the eldest surviving son of Charles Seymour (1621–1665), whose father Sir Francis Seymour (c. 1590–1664), a younger brother of the 2nd Duke of Somerset, had been created Baron Seymour of Trowbridge in 1641. When the 5th Duke died unmarried in 1678, the title passed to his brother, Charles Seymour (1662–1748), youngest son of the 2nd Baron Trowbridge. The 6th Duke, was known as "the Proud Duke",