World War I caused a conflict of loyalties for Charles Edward, but he finally decided to support the German Empire. He broke off relations with his family at the British and Belgian courts. This did not suffice to overcome doubts about his loyalties in Germany. Charles Edward served on the staff of an infantry division of the German army at the beginning of the war, fighting Russians in Prussia. In 1915, he had to stop due to rheumatism. Although he never held a command, he visited both the western and eastern fronts numerous times. Soldiers from his duchies were awarded the "Carl-Eduard-Kriegskreuz". In 1915, King George V, his cousin, ordered his name removed from the register of the Most Noble Order of the Garter.