Meantime, however, the king's brother and sister-in-law had aroused the Lutherans; the Swedish bishops were banded against him, and finally, when the king learned that none of his demands had been granted, except that of keeping the confiscated ecclesiastical property, he lost courage and reverted to Protestantism. The assurance given him by Possevin that he could rely on the help of Spain, of the Emperor, and of the Catholic princes of Germany did not move him. He saw before him the revolt of his subjects, and the accession of his brother; and, while insisting that he was a Catholic at heart, he refused to act, unless the Pope granted all his demands. On February 19 he convoked a Diet at Wadstena, at which Possevin was present, but as the majority was clearly against returning to the old Faith, the legate had to be satisfied with being merely an onlooker, while the king, convinced that he was acting against his conscience, yielded to the popular clamor. Another Diet was held with the same result. Meantime, the legate remained in Stockholm, devoting himself to the sick and dying, in a pestilence that was then devastating the city. He also succeeded in so strengthening the faith of the young Sigismund, the heir apparent, that when there was question subsequently of his renouncing Catholicity in order to ascend the throne, he had the courage to say that he would relinquish all his rights and withdraw into private life, rather than abandon the Faith. A much more curious exercise of diplomacy came in Possevin's way in the quarrel between the King of Poland and the ruler of Muscovy. The latter had made vast conquests in the East, and then turned his attention to Livonia, which was Polish territory. Bathori, who was ruler of Poland, met and conquered the invader in a series of successful battles. Whereupon the Czar, knowing Bathori's devotion to the Holy See, asked the Sovereign Pontiff, Gregory XIII, to intervene. Possevin was again called upon, and set out as plenipotentiary to arrange peace between the two nations. Incidentally, the intention of the Pope was to obtain the toleration of Catholics in the Russian dominions, to secure a safe passage for missionaries to China through Russia, to induce the Czar to unite with the Christian princes against the Turks, and even to bring about a union of the Greek and Latin churches.