BARNIM XI  . (1501-1573), son of Bogislaus X., duke of Pomerania, became duke on his father's death in 1523 . He ruled for a time in common with his elder brother George; and after George's death in 1531 he shared the duchy with his nephew Philip I., retaining for himself the duchy of Pomerania-Stettin . The earlier years of his rule were troubled by a quarrel with the margrave of Brandenburg, who wished to annex Pomerania . In 1529, however, a treaty was made which freed Pomerania from the supremacy of Brandenburg on condition that if the ducal family became extinct the duchy should revert to Brandenburg . Barnim adopted the doctrines of Martin Luther, and joined the league of Schmalkalden, but took no part in the subsequent war . But as this attitude left him without supporters he was obliged to submit to the emperor Charles V., to pay a heavy fine, and to accept the Interim, issued from Augsburg in May 1548 .