The Sixtus Affair, however, led to Count von Czernin's downfall. Emperor Karl I, using his brother-in-law Prince Sixte of Bourbon-Parma as his intermediary, had secretly assured French President Poincaré by a letter dated 24 March 1917 that he would support France's "just demand" for the return of Alsace-Lorraine. Although his role in the affair remains unclear, he was aware of the secret negotiations, although not of the exact wording of the letter. When French Premier Clemenceau published the letter a year later Count von Czernin, feeling himself betrayed by Emperor Karl I and on the verge of a nervous breakdown, tendered his resignation on 14 April 1918.