Frederick Stewart, 4th Marquess of Londonderry

Frederick William Robert Stewart, 4th Marquess of Londonderry (7 July 1805 – 25 November 1872), styled Viscount Castlereagh between 1822 and 1854, was a British nobleman and Tory politician. He was briefly Vice-Chamberlain of the Household under Sir Robert Peel between December 1834 and April 1835.

Background and education
Stewart was born at Grosvenor Square, Mayfair, London, the eldest son of Charles Stewart, 3rd Marquess of Londonderry, by his first wife Lady Catherine Bligh, daughter of John Bligh, 3rd Earl of Darnley. His mother died when he was seven and while his father was serving in the army overseas, Stewart was looked after by his uncle and aunt, Lord and Lady Castlereagh. He went to Eton in 1814, where he stayed until 1820. After his father succeeded to the marquessate of Londonderry in 1822, Stewart became known by the courtesy title Viscount Castlereagh.

Political career
Lord Castlereagh sat as Member of Parliament for County Down from 1826 to 1852. He served under the Duke of Wellington as a Lord of the Admiralty from 1828 to 1830 and under Sir Robert Peel as Vice-Chamberlain of the Household from December 1834 to April 1835. On 23 February 1835 he was sworn of the Privy Council. He was one of the Members of Parliament for County Down from 1826 until 1852. By the latter year, he "had fallen out with his father, the Marquess of Londonderry over their views on the land question [and] was obliged to retire because of these differences". From 1845 until 1864 he was Lord Lieutenant of Down. In 1856 he was made a Knight of the Order of St Patrick.

Personal life
In 1838, Count Gérard de Melcy the husband of Giulia Grisi the Italian operatic singer 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.

Lord Londonderry 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 died at the White Rock Pavilion (this was almost certainly White Rock Villa as the White Rock Pavilion, now called the White Rock Theatre, wasn't built until 1927) in Hastings in November 1872, aged 67, and was succeeded in the marquessate by his half-brother, George Vane-Tempest, 2nd Earl Vane. The Marchioness of Londonderry died on 2 September 1884, aged 70, and was buried with him in Newtownards.