The Gordons of Cluny were implicated in the Jacobite Rising of 1745, and had also incurred debts. This resulted in the castle passing to a third branch of the Gordon family around 1753, although the exact date is unknown. The new proprietor John Gordon (1695–1769) was of obscure origins. He was an Edinburgh merchant as well as a factor to Cosmo Gordon, 3rd Duke of Gordon. John Gordon's son was also named Cosmo Gordon (1736–1800) and he inherited the estate on his father's death in 1769. He was a politician and co-founder of the Royal Society of Edinburgh. He did some work at the castle, although records give no indication of what was involved. Plans for a re-design were commissioned from Robert Adam in 1790 and from his business partner and younger brother James in 1793, though this work was never carried out. Pre-deceased by his wife, Mary Baillie, Cosmo Gordon died without issue in 1800 and was succeeded by his brother Charles, described by architectural historian H. Gordon Slade as "eccentric and excessively penurious". When Charles died on 8 May 1814, various bequests were made to his children; his eldest son John, later an army colonel and a member of Parliament, inherited Cluny and the remainder of the properties plus £30,000. No money had been spent on the estate during the years it was owned by Charles Gordon.