In 1838, Count Gérard de Melcy, the husband of the Italian operatic singer
Giulia Grisi, discovered a letter written to Giulia by Frederick Stewart, and the two men fought a duel on 16 June of that year. Lord Castlereagh was wounded in the wrist; the Count was uninjured. After the duel, Grisi left her husband and began an affair with Lord Castlereagh. Their son,
George Frederick Ormsby (1838–1901), was born in November 1838 and brought up by his father. By 1852, he "had fallen out with his father,
the 3rd Marquess of Londonderry, over their views on the land question [and] was obliged to retire because of these differences". Frederick Stewart married Lady Elizabeth Frances Charlotte Jocelyn, widow of
Viscount Powerscourt and daughter of
Robert Jocelyn, 3rd Earl of Roden, at the British Embassy in Paris on 2 May 1846. There were no children from the marriage. In 1855 his wife converted to
Roman Catholicism. He succeeded his father in 1854 as the
4th Marquess of Londonderry. He built
Scrabo Tower as a monument to the memory of his father. In 1857 he and his wife attended the ceremony of the laying of the foundation stone. == Decline, death, and succession ==