In August 1878, Russian Tsar Alexander II, William's nephew, wrote a letter (known as "Ohrfeigenbrief") to him complaining about the treatment Russian interests had received at the Congress of Berlin. In response William, his wife Augusta, and his son the crown prince travelled to Russia (against the advice of Bismarck) to mend fences in face-to-face talks. However, by once again threatening to resign, Bismarck overcame the opposition of William to a closer alliance with Austria. In October, William agreed to the Dual Alliance ("Zweibund") between Germany and Austria-Hungary, which was directed against Russia.