The Most Honourable The Marquess of Londonderry KP PC
Portrait bySimon Jacques Rochard, 1833
Tenure	1854–1872
Predecessor	Charles Vane, 3rd Marquess of Londonderry
Successor	George Vane-Tempest, 5th Marquess of Londonderry
Born	7 July 1805 Grosvenor Square,Mayfair, London
Died	25 November 1872(1872-11-25) (aged 67) White Rock Pavilion,Hastings,Kent
Buried	Newtownards Priory
Spouse	Lady Elizabeth Jocelyn
Father	Charles Vane, 3rd Marquess of Londonderry
Mother	Catherine Bligh

Frederick William Robert Stewart, 4th Marquess of Londonderry (7 July 1805 – 25 November 1872), styledViscount Castlereagh from 1822 to 1854, was a British nobleman andTory politician. He was brieflyVice-Chamberlain of the Household underSir Robert Peel between December 1834 and April 1835.

Frederick Stewart was born on 7 July 1805 atGrosvenor Square,Mayfair, London.^[1] He was the only child ofCharles Stewart and his first wife Catherine Bligh. His father would become the 3rdMarquess of Londonderry but was at the time only the second son ofRobert Stewart, 1st Marquess of Londonderry. His father's family wasUlster-Scots. Frederick's mother was the fourth and youngest daughter ofJohn Bligh, 3rd Earl of Darnley.^[2]

He was his father's only son from his father's first marriage. In 1812, while Frederick's father was serving in thearmy in thePeninsular War, Frederick's mother died. Frederick was seven. His father remarried seven years later in 1819 and Frederick's half-siblings were born.

He was the only child of his parents but had younger half-siblings:

Following the death of his mother and during his father's absence on military and diplomatic duties, Frederick was largely raised by his uncle and aunt,Lord andLady Castlereagh. He went toEton in 1814, where he stayed until 1820. After his father succeeded to the marquessate of Londonderry in 1822, Frederick Stewart became known by thecourtesy titleViscount Castlereagh, which was to be his title for 32 years until 1854. He matriculated atChrist Church, Oxford, in 1823.^[5]

He served under theDuke of Wellington as aLord of the Admiralty from 1828 to 1830 and underSir Robert Peel asVice-Chamberlain of the Household from December 1834^[6] to April 1835. On 23 February 1835, he was sworn of thePrivy Council of the United Kingdom.^[7]

He was one of theMembers of Parliament forCounty Down from 1826 until 1852.^[8][9]

From 1845 until 1864 he wasLord Lieutenant of Down. In 1856 he was made a Knight of theOrder of St Patrick.

In 1838, Count Gérard de Melcy, the husband of the Italian operatic singerGiulia 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".^[10]

Frederick Stewart married Lady Elizabeth Frances Charlotte Jocelyn, widow ofViscount Powerscourt and daughter ofRobert 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 toRoman Catholicism.^[11]

He succeeded his father in 1854 as the4th Marquess of Londonderry. He builtScrabo Tower as a monument to the memory of his father.^[12] In 1857 he and his wife attended the ceremony of the laying of the foundation stone.^[13]

In 1862 Londonderry was diagnosed as mentally ill. He was secluded in a mental institution at White Rock Pavilion inHastings.^[15][b] He died there on 25 November 1872, aged 67 and was buried in theNewtownards Priory. His wife, the dowager Marchioness of Londonderry, died on 2 September 1884, aged 70, and was buried with him in the double grave in the priory.

As he had no legitimate children, he was succeeded in the marquessate by his half-brother,George Vane-Tempest, 2nd Earl Vane. This had the effect that the fortunes of the Stewart and the Vane side of the Londonderry family were reunited in a single hand.

• Hansard 1803–2005:contributions in Parliament by the Marquess of Londonderry

• 1805 births
• 1872 deaths
• Bligh family
• Knights of St Patrick
• Lord-lieutenants of Down
• Lords of the Admiralty
• Marquesses of Londonderry
• Members of the Parliament of the United Kingdom for County Down constituencies (1801–1922)
• Members of the Privy Council of the United Kingdom
• People educated at Eton College
• UK MPs 1826–1830
• UK MPs 1830–1831
• UK MPs 1831–1832
• UK MPs 1832–1835
• UK MPs 1835–1837
• UK MPs 1837–1841
• UK MPs 1841–1847
• UK MPs 1847–1852
• UK MPs who inherited peerages
• Vane-Tempest-Stewart family

• Articles with short description
• Short description is different from Wikidata
• Use British English from March 2020
• All Wikipedia articles written in British English
• Use dmy dates from September 2021