Eric was intent upon making a great match, wooing Elizabeth of England, Mary Stuart of Scotland, Renata of Lothringia and Christine of Hesse, with more or less success, overlooking Margaret of Valois, who was anxious to marry him. His mistress, Carin Monsdotter, a child of the people, but beautiful and of a noble character, for whom he had formed a secret attachment, finally was made his queen.
The German Order which held Esthonia and Livonia suffered during this period considerably through Russian invasions. The town of Reval, with a large part of Esthonia, was ceded to Sweden in 1562, upon the receipt of a loan, Eric immediately giving his attention to the depressed and enslaved peasants of that section. Later the grandmaster of the Order turned Livonia over to the king of Poland, who, in need of money, placed seven castles of this province at the disposal of John, duke of Finland. John had tendered a loan to the Polish king and married his sister Catherine. Eric considered these negotiations as harmful to his royal authority, and he asked his brother to give account of them in person. John refused, making the royal emissaries his prisoners. The Swedish Riksdag condemned John to death for high treason, and an army was despatched to Finland, which carried back Duke John and his consort as prisoners. John’s sentence was commuted to imprisonment at Gripsholm, proud Catherine choosing to share the fate of her husband (1563). The prison life of the ducal couple at Gripsholm was not an unpleasant one. They enjoyed a great deal of liberty and luxury at the splendid castle in Lake Mælar, King Eric sending his brother a copy of Boccaccio’s “Decamerone” in German, to read for a pastime. The duke read the work and translated it into Swedish. The room called “king John’s prison,” which is still preserved with the artistic decoration which Duke Charles later bestowed on it, served as sleeping apartment for the prisoners, and there Catherine gave life to two children, one of whom was to become the founder of the Polish line of Vasa kings. It is said that Duke Magnus became a prey to the disposition of insanity latent in his family, by being forced to sign the death sentence of his brother John, King Eric being anxious of having him share the responsibility. Magnus lived until quite an advanced age, but was never cured of his mental ailment. Even in his best hours he was not of very bright intellect. While sojourning at the castle of Vadstena, by the Lake Vetter, he had the vision of a mermaid, who coaxed him to follow her. The duke jumped from the window of his apartment into the moat below. He did not sustain any serious injury, but the incident made the unhappy prince famous in tradition and song.