His paternal grandfather was Henry Cadogan of Llanbetter, a grandson of Thomas Cadogan, of Dunster, who claimed descent from the ancient princes of Wales (called Cadwgan ap Elystan Glodrydd "The Renowned", Prince of Fferreg, of Dol-y-Gaer,
Breconshire).[2]
^William Cadogan, 1st Earl Cadogan was a noted soldier, politician and diplomat. He was a general in the army and fought in the
War of the Spanish Succession and also served as
Ambassador to the Netherlands and as
Master-General of the Ordnance. In 1716, he was raised to the Peerage of Great Britain as Baron Cadogan, of Reading in the County of Berkshire, with normal remainder to the heirs male of his body. In 1718, he was further honoured when he was made Baron Cadogan, of
Oakley in the County of Buckingham, with remainder, failing heirs male of his own, to his younger brother
Charles Cadogan and the heirs male of his body, and Viscount Caversham, in the County of Oxford, and Earl Cadogan, in the County of Denbigh, with remainder to the heirs male of his body. These titles were also in the Peerage of Great Britain.[2]