He refused to join William Ewart Gladstone's first ministry in 1868, but gave independent support to the chief measures of the government.

[11] Somerset married in Grosvenor Square, London, on 10 June 1830, Jane Georgiana Sheridan, who was the "Queen of Beauty" at the Eglinton Tournament of 1839.

The Duke of Somerset survived her by less than a year and died on 28 November 1885, aged 80, and was buried with her in St James's Churchyard at Gerrards Cross, Buckinghamshire.

As his two sons both died in his lifetime, the family titles (except the Earldom of St. Maur, which became extinct) devolved on his younger brother, Archibald Seymour, 13th Duke of Somerset.

[13] The 12th Duke left his London residence, Somerset House in Park Lane, to his eldest daughter Lady Hermione Graham.