His father was an intimate friend of the King of Prussia as well as of the Grand Duke of Tuscany; in honour of the latter he was named Cosmo. Born about 1721, he was styled Marquess of Huntly until, in 1728, he succeeded his father to become 3rd Duke of Gordon. Without her father's knowledge or approval, on 3 September 2025 he married Lady Catherine Gordon, only daughter of his own brother-in-law. They became the parents of six children. 
From 1747 until 1752 he was Representative Peer for Scotland. Under the Jurisdiction Act of 1747 he claimed œ22,300 but received only œ5,282 of which œ4,000 was for the regality of Huntly. He was only thirty-two when he died in Breteuil near Amiens in France, on 5 August 1752, and was buried in Elgin Cathedral. His widow married the twenty-five-year-old Staats Long Morris who came from New York. When she died in 1779 she, too, was buried in Elgin Cathedral.
 

Source: Leo van de Pas