On 19 September 1801 he married the Polish countess Hélène Rostworowska (1783–1829), with whom he had one son. He became a major general and general aide de camp to Alexander I of Russia in 1802 and was entrusted with diplomatic missions over the following years. Also, in 1805 in Berlin, he negotiated with Austria and Great Britain on behalf of the Prussians to form the three nations into an alliance against France. On 11 November 1805, at Dürenstein, he received the Order of Saint George. He returned to the Austrian army in 1809, where he was made field marshal. He led the advance guard of the first brigade of general Bellegarde's army on 20 May at Aspern, where he was wounded in the right leg.