After the Swedish king Erik XIV had become insane and murdered leading aristocrats in late 1567, his brother duke John (the later king John III) assumed control of the kingdom and had Erik imprisoned. When this was accomplished, he sent a delegation to Denmark to negotiate for an end of the Northern Seven Years' War inherited from his brother. Frederik II of Denmark was unable to exploit the inner-Swedish conflict, as his treasures were emptied by the costs of his German mercenary armies, on whom he had relied throughout the war, and the rebuilding of the Danish navy, finished by the summer of 1567, after a large part of it had sunk in a storm in July 1566. Furthermore, duke John maintained amicable relations to Sigismund II Augustus of Poland-Lithuania, thwarting hopes for an anti-Swedish