General von Plessen also held the office of His Majesty's Orderly Adjutant General () to Kaiser Wilhelm II, thus making him one of the Emperor's closest confidants. By 1918 he was the oldest serving officer in the Imperial German Army, although Paul von Hindenburg falsely claimed this for himself. In 1918, von Plessen was awarded the Pour le Mérite, Germany's highest military honor. He remained devoted to the Kaiser until the collapse of the monarchy in November, 1918.