 He was later reassigned to his position as Prussian ambassador in London, and, after 1871, as German Imperial ambassador with the rank of minister of state, which he remained until his death in 1873.During this time, he also served as the Prussian delegate at the London Peace Conference of 1864, which led to the signing of the Treaty of Vienna.In 1867, he was also the ambassador of the North German Confederation at the negotiations for the Treaty of London, which determined the status of Luxembourg.