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
Charles Seymour, 6th Duke of Somerset of Hertford (1684–1749) had produced a son of his own, Lord Beauchamp (d.1744), who had predeceased him without progeny, and thus he had only a daughter and sole heiress Lady Elizabeth Seymour, who in 1740 had married Sir Hugh Smithson, 4th Baronet. Before the death of the 6th duke in 1748, it had thus become apparent that the dukedom of Somerset would devolve by law onto an extremely distant cousin and heir male, the 6th duke's 6th cousin Sir Edward Seymour, 6th Baronet (1695–1757) of Berry Pomeroy in Devon and of Maiden Bradley in Wiltshire, who in fact represented the