Dreikönigsbündnis
In October 1850, he traveled to the Warsaw Conference to meet with Czar Nicholas and sound out the Russian stance in the Austria-Prussia rivalry. Though he had initially supported the implementation of the Prussian-led Erfurt Union, he shied away from an armed conflict with Austria as State Chancellor Prince Felix of Schwarzenberg was able to strengthen the alliance with the Russian Empire isolating the Prussian side. After his return, Friedrich Wilhelm spoke out against mobilising the Prussian Army as advocated by Foreign Minister Joseph von Radowitz. Shortly afterwards, he took seriously ill and died, it is said from the humiliation of the Czar's abandonment of the Erfurt policy. He was buried in the crypt of Berlin Cathedral.