The three nations signed a secret treaty on 3 January 1815, agreeing to go to war against Russia and Prussia, if necessary, to prevent the Russo-Prussian plan from coming to fruition. When the Tsar heard of the secret treaty he agreed to a compromise that satisfied all parties on 24 October 1815. Russia received most of the Napoleonic Duchy of Warsaw as a "Kingdom of Poland" – called Congress Poland, with the tsar as a king ruling it independently of Russia. Furthermore, the tsar was unable to unite the new domain with the parts of Poland that had been incorporated into Russia in the 1790s. Prussia received 60 percent of Saxony-later known as the Province of Saxony, with the remainder returned to King Frederick Augustus I as his Kingdom of Saxony.