The Danish mercenary army was superior to the Swedish peasant army, but the professional army would not fight until their pay was current. Because only a fraction of the army would march, Denmark had to give up the plan to take the fortress of Kalmar and settle for an attack on Stockholm instead. In August 1564, Eric attacked Blekinge and his army occupied it cruelly , though the Danish later reclaimed this. Eric XIV turned insane, paralyzing the Swedish war effort. The Danish were exhausted and made no serious attacks until Rantzau attacked Småland and Östergötland with about 8,500 men. He burned every field and house and destroyed every head of livestock he could. An attempt to cut off his retreat over the Holaveden failed, and in the middle of February 1568 he returned to Halland. Attempts were made to make peace between the fighting nations during these years. Negotiators included the dukes of Pomerania, French messenger Charles Dancay, and Holy Roman Emperors Ferdinand I and Maximilian II. The emperors wanted Denmark and Sweden to give back the territories won in Livonia, during the ongoing Livonian War, but Sweden refused to give in to those demands. In 1568, the Swedish duke John staged a successful coup d'etat against his brother, King Eric. Enthroned as king with the name John III, he began negotiations with Denmark, and on 18 November the same year this led to a draft peace agreement in Roskilde. This was turned down by the Swedes, however, and in 1569 war stirred again. The Danes attacked and reclaimed Varberg, on 13 November. The Swedes on the other hand now had great success in Skåne.
Question: What title did King Eric XIV's brother have before he became king?
Answer: duke