George Spencer-Churchill, 6th Duke of Marlborough (né Spencer; 27 December 1793 – 1 July 1857), styled Earl of Sunderland until 1817 and Marquess of Blandford between 1817 and 1840, was a British nobleman, politician, and peer.

In response to the Roman Catholic Relief Act 1829, Blandford introduced the first major reform bill in February 1830, calling for transfer of rotten borough seats to the counties and large towns, disfranchisement of non-resident voters, prevention of holders of office under the Crown from sitting in Parliament, payment of a salary to MPs, and the general franchise for men who owned property.

Henry Jeffrey Flower, 4th Viscount Ashbrook, the father of his second wife, was a founder member of the Squadron, and his family participated in the Cowes social scene.

[12] Child by Harriet Caroline Octavia Spencer, who subsequently married her cousin, Count Karl Theodor von Westerholt (1795–1863), son of Count Alexander von Westerholt, in 1819:[11] He married, firstly, his first cousin Lady Jane Stewart (1798–1844), daughter of George Stewart, 8th Earl of Galloway, on 13 January 1819.

They had two children: After his second wife's death in April 1850, aged 31, he married, thirdly, his first cousin Jane Frances Clinton Stewart (1818–1897),[13] daughter of the Hon.