Albert became Duke of Prussia after paying feudal homage to his cousin, the King of Poland, Sigismund Augustus, on 19 July 1569 in Lublin.[1] The homage was described by the Polish chronicler Jan Kochanowski in his work Proporzec ("Standard"). During the 1573 Polish election, Albert Frederick attempted to gain acceptance to the Polish senate but was opposed by the powerful Jan Zamoyski (later Grand Hetman of the Crown of the Kingdom of Poland) who feared the influence of Protestants in the Polish legislative body. Albert Frederick initially refused to recognize the election of Stefan Bathory and supported the candidacy of Maximilian of Austria. However, at the Toruńsejm of October 1576 he gave his support to the new monarch.
As the great-grandson of the Polish king Casimir IV Jagiellon, and as a Duke in Prussia who was fluent in Polish, Albert Frederick was seriously considered for a time as a possible candidate for the Polish throne. He particularly enjoyed the support of Polish Lutherans.
In 1572 he began to exhibit signs of mental disorder. He had twice tried to commit suicide and was prone to violent outbursts and held a great fear of " Turks and Muscovites " overrunning Germany.
In early 1578, the regency was taken over by his cousin, George Frederick of Brandenburg-Kulmbach (1539–1603). After George Frederick's death in 1603, the Polish king Sigismund III Vasa appointed Joachim Frederick as regent in 1605, and permitted his son, John Sigismund, to succeed him in 1611. The latter became Duke of Prussia after Albert Frederick's death in 1618.[2]
