In 1923 Clark and his brother Sterling entered into a famous feud that lasted until their deaths. The terms of their father's trust limited the beneficiaries to the four brothers and their issue. Sterling, who was childless and had married his long-term French mistress in 1919, sought to change the terms of the trust to make her a beneficiary. Clark, the only one of the brothers who had fathered children, refused to agree to the change. Sterling withdrew his quarter of the trust's assets, sold his properties in Cooperstown, and never spoke to Clark again.