Editing Duchy of Prussia (section)

===Lack of heirs===
When Albert died in 1568, his teenage son (the exact age is unknown) [[Albert Frederick, Duke of Prussia|Albert Frederick]] inherited the duchy. Sigismund II was also Albert Frederick's cousin. The [[Elector of Brandenburg]] [[Joachim II Hector, Elector of Brandenburg|Joachim II]], converted to Lutheranism in 1539. Joachim wanted to merge his lands with the Prussian dukedom so that his heirs would inherit both. Joachim petitioned his brother-in-law, king [[Sigismund II Augustus|Sigismund II]] of Poland the co-enfeoffment of his line of the Hohenzollern with the Prussian dukedom, and finally succeeded, including the then usual expenses.

On 19 July 1569, when, in [[Lublin]], Poland, duke Albert Frederick rendered King Sigismund II [[homage (feudal)|homage]] and was in return [[enfeoffment|installed]] as Duke of Prussia in [[Lublin]], the King simultaneously enfeoffed Joachim II and his descendants as co-heirs.

Administration in the duchy declined as Albert Frederick became increasingly feeble-minded, which led Margrave [[George Frederick, Margrave of Brandenburg-Ansbach|George Frederick]] of [[Brandenburg-Ansbach]] to become [[Regent]] of Prussia in 1577.

Following King [[Sigismund III Vasa|Sigismund III]]'s Prussian regency agreement (1605) with [[Joachim Frederick, Elector of Brandenburg|Joachim Frederick of Brandenburg]] and his [[Treaty of Warsaw (1611)|Treaty of Warsaw]], 1611, with [[John Sigismund, Elector of Brandenburg|John Sigismund of Brandenburg]], confirming the Brandenburgian co-inheritance of Prussia, both regents guaranteed the free practice of Catholic religion in predominantly-Lutheran Prussia. Based on the agreements, some Lutheran churches were reconsecrated as Catholic places of worship (e.g. [[St. Nicholas Cathedral, Elbląg|St. Nicholas Church]], [[Elbląg]] in 1612).