His paternal grandfather was Ivor Guest, 1st Baron Wimborne (1835–1914), a Welsh industrialist.

His great-grandfather was John Spencer-Churchill, 7th Duke of Marlborough, making him a first cousin once removed of British Prime Minister Winston Churchill.

[2] His brother, Raymond R. Guest (1907–1991), was the United States Ambassador to Ireland from 1965 to 1968,[3] who married three times.

[6] In 1919, his parents entered into a separation agreement and his mother received custody of him, thereafter living in the United States.

He was the only player in the history of the Indoor Polo Association with the top rating of ten goals.