Question: When did the man who Lord Frederick Charles Cavendish was a protege of last serve as Prime Minister?

Context articles: Cavendish River
Lord Frederick Cavendish (British Army officer)
Phoenix Park Killings
Frederick C. Alderdice
Charles Greville (diarist)
Cavendish memorial fountain
Lord Frederick Cavendish
Lord Frederick Cambridge
Charles Cavendish, 3rd Baron Chesham
William Ewart Gladstone

The Cavendish River is a river of New Zealand.
 It is one of the southernmost rivers of the country's South Island, flowing south for 15 km to reach Foveaux Strait on the southern coast of Fiordland.
 The river was named in 1882 by John Hay in commemoration of Lord Frederick Cavendish, who earlier that year was murdered in Dublin's Phoenix Park.
Field Marshal Lord Frederick Cavendish (August 1729 – 21 October 1803) was a British Army officer and Whig politician.
 After serving as an aide-de-camp to the Duke of Cumberland in Germany during the early stages of the Seven Years' War, he served under Charles Spencer, 3rd Duke of Marlborough during in the raid on St Malo and then took part in the raid on Cherbourg.
 Cavendish commanded the rear-guard during the re-embarkation following the disastrous battle of Saint Cast and was taken prisoner.
 After his release, Prince Ferdinand of Brunswick gave him command of a brigade of chasseurs which he led to victory at the Battle of Wilhelmsthal in June 1762.
The Phoenix Park Killings were the fatal stabbings of Lord Frederick Cavendish and Thomas Henry Burke in Phoenix Park in Dublin on 6 May 1882.
 Cavendish was the newly appointed Chief Secretary for Ireland, and Burke was the Permanent Undersecretary, the most senior Irish civil servant.
 The assassination was carried out by members of the rebel group Irish National Invincibles, a more radical breakway from the Irish Republican Brotherhood.
Frederick Charles Alderdice (November 10, 1871 – February 26, 1936) was a Newfoundland businessman, politician and the last Prime Minister of Newfoundland.
 Alderdice was born in Belfast, Ireland and was educated at Methodist College Belfast.
 He moved to Newfoundland in 1886.
 A prominent St. John's businessman, Alderdice was appointed to the Legislative Council of Newfoundland (the Upper House of the legislature) in 1924 and became leader of the Liberal-Conservative Progressive Party and the dominion's Prime Minister when his cousin Walter Stanley Monroe retired from the post on August 15, 1928.
 Alderdice's first term as Prime Minister was short-lived, however, as his government lost that year's general election to the Liberals led by Sir Richard Squires.
Charles Cavendish Fulke Greville (2 April 1794 – 17 January 1865) was an English diarist and an amateur cricketer who played first-class cricket from 1819 to 1827.
 His father Charles Greville was a second cousin of the 1st Earl of Warwick, and his mother was Lady Charlotte Bentinck, daughter of the 3rd Duke of Portland (former leader of the Whig party and Prime Minister).
The Cavendish memorial fountain is a drinking fountain erected in 1886 at Bolton Abbey, North Yorkshire, England as a memorial to Lord Frederick Cavendish following his murder in Phoenix Park by the Irish National Invincibles in May 1882.
 The fountain is a Grade II listed building.
Lord Frederick Charles Cavendish {'1': ", '2': ", '3': ", '4': "} (30 November 1836 – 6 May 1882) was an English Liberal politician and "protégé" of the Prime Minister, William Ewart Gladstone.
 Cavendish was appointed Chief Secretary for Ireland in May 1882 but was murdered only hours after his arrival in Dublin, a victim of the politically motivated Phoenix Park murders.
Lord Frederick Cambridge ("Frederick Charles Edward") (born Prince Frederick of Teck) (24 September 1907 – 15 May 1940) was a descendant of the British Royal Family.
 He was the younger son of the Adolphus Cambridge, 1st Marquess of Cambridge, formerly the Duke of Teck, and a nephew of Queen Mary, the consort of King George V.
Brigadier General Charles Compton William Cavendish, 3rd Baron Chesham {'1': ", '2': ", '3': ", '4': "} (13 December 1850 – 9 November 1907), styled The Honourable Charles Cavendish between 1863 and 1882, was a British soldier, courtier and Conservative politician.
 He served as the last Master of the Buckhounds under Lord Salisbury from 1900 to 1901.
William Ewart Gladstone, ( ; 29 December 1809 – 19 May 1898) was a British Liberal statesman and earlier Conservative politician.
 In a career lasting over 60 years, he served as Prime Minister four separate times (1868–74, 1880–85, February–July 1886 and 1892–94), more than any other person, and served as Chancellor of the Exchequer four times.
 Gladstone was also Britain's oldest Prime Minister; he resigned for the final time when he was 84 years old.