John Seymour, 4th Duke of Somerset (bef. 1646–1675), fourth and youngest son of the 2nd Duke, died without issue Francis Seymour, 5th Duke of Somerset (1658–1678), great-grandson of Edward Seymour, Viscount Beauchamp through the Lords Seymour of Trowbridge ; himself eldest son of the 1st Duke's fourth son; Edward Seymour, 1st Earl of Hertford ; died without issue