Marriages and descendants
Somerset married twice. Firstly, in 1682, at the age of twenty, as described above, he married the 15-year-old heiress Lady Elizabeth Percy (1667–1722), already twice widowed. As Duchess of Somerset, she served as Groom of the Stole and First Lady of the Bedchamber at the court of Queen Anne.
Following his wife's death in 1722 the Duke developed a romantic attachment to the widowed Sarah Churchill, Duchess of Marlborough (1660–1744) (née Sarah Jennings) whose husband John Churchill, 1st Duke of Marlborough had died the same year. He sent her "feverish love letters", but she remained loyal to her late husband.
By Lady Elizabeth Percy he had one surviving son and three daughters:
Charles Seymour, Earl of Hereford (baptized 22 March 1683 – died before 26 August 1683), who died an infant in his first year.
Algernon Seymour, 7th Duke of Somerset (11 November 1684 – 7 February 1750), eldest surviving son and heir, known during his father's lifetime by the courtesy title of Earl of Hertford, one of his father's subsidiary titles. Algernon's only daughter and sole-heiress Lady Elizabeth Seymour, suo jure Baroness Percy, together with her husband Sir Hugh Smithson, 4th Baronet (died 1786) (who in 1749 adopted the surname Percy and in 1766 was created Duke of Northumberland) inherited half the great Percy estates including Alnwick Castle and Syon House.
Percy Seymour, died unmarried.
Lady Elizabeth Seymour (1685 – 2 April 1734), eldest daughter, wife of Henry O'Brien, 8th Earl of Thomond (1688–1741), without progeny. His chosen heir was her younger nephew Percy Wyndham-O'Brien, 1st Earl of Thomond (c. 1713–1774) of Shortgrove, Essex, who adopted the surname O'Brien and was elevated to the peerage as Earl of Thomond.
Lady Catherine Seymour (1693 – 9 April 1731), 2nd daughter, wife of Sir William Wyndham, 3rd Baronet (c. 1688–1740) of Orchard Wyndham in Somerset. He was a radical Tory and leader of the Jacobite rebellion of 1715 against King George I, but nevertheless remained a firm favourite of his father-in-law the 6th Duke of Somerset, a firm supporter of the Hanoverian Succession and a Whig. Following his arrest in 1715 for high treason and his imprisonment in the Tower of London, the Duke offered to provide bail for his liberty, which was badly received by the King, who shortly afterwards dismissed him as Master of the Horse. Her eldest son was Charles Wyndham, 2nd Earl of Egremont (1710–1763), who inherited half of the great Percy estates including Petworth House, Egremont Castle in Cumberland and Leconfield Castle in Yorkshire.
Lady Anne Seymour (1709 – 27 November 1722), 3rd daughter, who married (as his second wife) Peregrine Osborne, Marquess of Carmarthen (1691–1731), later 3rd Duke of Leeds, by whom she had a son who died an infant. She died aged 13 without surviving progeny.
Lady Frances Seymour, died unmarried.
Secondly on 4 February 1725, at the age of 63 he married Lady Charlotte Finch (1693–1773), a daughter of Daniel Finch, 7th Earl of Winchilsea, later 2nd Earl of Nottingham. He treated her poorly and once told her, after she had gently tapped him on the shoulder with her fan: "Madam, my first wife was a Percy and she never took such a liberty". By Charlotte Finch he had two further children:
Lady Frances Seymour (18 July 1728 – 25 January 1761), wife of John Manners, Marquess of Granby, eldest son of the Duke of Rutland
Lady Charlotte Seymour (21 September 1730 – 15 February 1805), wife of Heneage Finch, 3rd Earl of Aylesford and had issue.
Somerset's last known letter to Sarah Churchill, Duchess of Marlborough, dated 1737, twelve years after his second marriage, declared his unchanged affections for her. The correspondence is preserved in the British Library.
