He was the son of Ivor Grosvenor Guest, 2nd Viscount Wimborne (1903–1967) and his wife Lady Mabel Edith Fox-Strangways, a daughter of Giles Fox-Strangways, 6th Earl of Ilchester.
William Walton composed "Set me as a seal upon thine heart" for his parents' wedding.
[2] His paternal grandfather was Ivor Guest, 1st Viscount Wimborne (1873–1939), who was a British politician and one of the last Lords Lieutenant of Ireland, serving in that position at the time of the Easter Rising in 1916.
Together they had: He later married Venetia Margaret Barker (nee Quarry); his sister-in-law was Miranda Macmillan, Countess of Stockton (1947-2020).
Together, they had: His widow, now Dowager Viscountess Wimborne, lives at Fontaine-l'Abbé, France.