John Reginald Lopes Yarde-Buller, 3rd Baron Churston OBE, MVO, (9 November 1873 – 19 April 1930) was a British peer and soldier. He is the grandfather of Karim Aga Khan, leader of the Nizari Ismailis, an Islamic sect.

Yarde-Buller was born on 9 November 1873. He was the only son of the John Yarde-Buller, 2nd Baron Churston and Barbara Yelverton. His mother was the only child of Sir Hastings Yelverton and the 20th Baroness Grey de Ruthyn.^[1]

He was educated at Winchester College.^[2]

Yarde-Buller was commissioned a second-lieutenant in the Scots Guards on 8 April 1896 and promoted to lieutenant on 13 April 1898. Following the outbreak of the Second Boer War in late 1899, Yarde-Buller was with the 2nd Battalion of his regiment as it left Southampton for South Africa on the SS Britannic in March 1900.^[3] On arrival, the battalion was attached to the 16th Infantry Brigade serving as part of the 8th Division under Sir Leslie Rundle. Yarde-Buller was present at operations in the Orange River Colony May–November 1900, including the action at Biddulphsberg in May 1900 and Wittebergen in July 1900.^[4]

After his return from the war, he was appointed aide-de-camp to The Lord Curzon, Viceroy of India in January 1902,^[5][6] and promoted to captain on 23 April 1902.^[7] He served in India until the following year, then as ADC to The Duke of Connaught from 1904 to 1906. He later became a lieutenant-colonel in the short-lived 3rd Resident Battalion of the Scots Guards.^[4]

On 24 April 1907, he married the music hall singer Jessie Denise Orme Smither, only daughter of Alfred John Smither.^[8] Before their divorce in 1928,^[9] they had six children, most of whom were known for their high-profile marriages and divorces:^[4][10]

• Hon. Joan Barbara Yarde-Buller (1908–1997), who married G/Capt Loel Guinness in 1927.^[11] They divorced in 1936 and she remarried to Prince Aly Khan.^[12] They too divorced, in 1949, and she married, thirdly, to the 2nd Viscount Camrose.^[13]
• Richard Francis Roger Yarde-Buller, 4th Baron Churston (1910–1991), who married three times.^[13]
• Hon. John Reginald Henry (1915–1962), soldier who married Guendolen Osborn Roots, daughter of Rev. Charles Roots, in 1939.^[13]
• Hon. Denise Margaret Yarde-Buller (1916–2005), who married the 5th Baron Ebury before divorcing in 1954.^[13]
• Hon. Lydia Yarde-Buller (1917–2006), who married John Russell, 13th Duke of Bedford.^[13]
• Hon. Primrose Lillian Yarde-Buller (1918–1970), who married the 7th Earl Cadogan before divorcing in 1960.^[13]

In 1910, Yarde-Buller inherited his father's title and he and his wife divorced in 1928.^[9] In 1926.^[14] When he died on 19 April 1930, his eldest son inherited his title. Lady Churston later married, and divorced Theodore William Wessel, the former Danish chargé d'affaires in Chile,^[15] before marrying the 7th Duke of Leinster in 1946.^[16]