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
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