duke to John the Younger (1589–1618), his newborn son in a second marriage to Gunilla Bielke (1568–1597). King Sigmund (III) of Poland and Sweden, half-brother of John the Younger, seems to have confirmed this appanage. A royal chancellery administered the duchy on behalf of the child-duke and provided him with his allotted revenues. However, when Duke John approached adulthood, his duchy was exchanged in 1606 for that of Östergötland which previously had been held by King John's brother, the late Duke Magnus. Duke John the Younger married his first cousin Princess Maria Elisabeth of Sweden (1596–1618). They died childless. From 1590 to 1599 John's father and half-brother (as most subsequent monarchs until 1720) continued to call themselves Grand Dukes of Finland. Gustav Adolf Crown Prince Gustav Adolf (1594–1632), elder son of Charles IX of Sweden, as heir apparent was made Duke of Finland in 1606, while Östergötland was assigned to his cousin Duke John the younger instead. Gustav Adolf then started to receive ducal revenues from Finland. When he ascended the throne of Sweden in 1611 he readopted Grand Duke of Finland among his titles. He was the last to have a real feudal principality of Finland and revenues therefrom. List of Dukes and Duchesses of Finland Includes Swedish Lords of Finland by other titles. No duke of Finland has left descendants in marital lines which survive today. Except John III's legitimate descent (kings of Sweden and Poland are totally extinct since 1672), lineage of all the others became extinct upon their own death or at the death of an only surviving legitimate child. See also Monarchy of Finland Grand Duchy of Finland Dukes of Swedish Provinces List of Finnish monarchs Governor-General of Finland References Medieval Finland Finland under Swedish rule Rulers of Finland Finland Finnish nobility