Duke John Adolphus died on 2 July 1704 in Ruhleben, a few days after his son, Adolphus Augustus, had been killed in a riding accident.
He was in Germany at the outbreak of the Great War and interned as a civil prisoner of war at Ruhleben.
Ruhleben internment camp - a World War I detention camp for enemy civilians
He was arrested in Berlin on November 6, 1914, and sent to Ruhleben, a civilian detention camp in the Spandau district.
During World War I, Keel was held in the civilian internment camp at Ruhleben in Germany, where he played an active role in the camp's musical life, giving many recitals to help boost the morale of his fellow detainees.