In January 1900 he was appointed in command of the 10th battalion of the Imperial Yeomanry (which included companies from Buckinghamshire, Berkshire and Oxfordshire), serving in the Second Boer War,[5] and received the temporary rank of colonel in the army.

Later that year, he was promoted to brigadier general and in November 1900 appointed a Knight Commander of the Order of the Bath (KCB) for his services[8] (he was invested by King Edward VII at Marlborough House on 25 July 1901 during a brief visit to London).

[10] After his return to the United Kingdom, he was in late April 1902 appointed Inspector General of Imperial Yeomanry (at Army Headquarters) with the temporary rank of major-general whilst so employed.

They had two sons and two daughters:[14] Lady Chesham joined her husband in South Africa in April 1900, travelling there on the SS Dunottar Castle with her two sisters the Duchess of Teck and the Marchioness of Ormonde.

[15] She was appointed a Lady of Grace of the Order of St. John (DStJ) in July 1901,[16] and in December the same year received the decoration of the Royal Red Cross (RRC) for her services with the Imperial Yeomanry Hospital during the Boer War.