In 1614, Anna Sophia was married to
Frederick Ulrich, Duke of Brunswick-Lüneburg. Seven years older than Anna Sophia, Friedrich much "
devoted to the pleasures of the table" was an alcoholic, who was so was so uninterested in ruling that he would sign any paper of government put before him without reading it. The marriage would turn out to be unhappy and childless. Between 1616 and 1622, owing to his diminished capability as a ruler, he was deposed by his mother (Anna Sophia's mother-in-law),
Elizabeth of Denmark, with the help of Frederick Julius' maternal uncle, King
Christian IV of Denmark. Anna Sophia and her mother-in-law did not got along. In 1620, Anna Sophia sheltered her sister Maria Eleonora in Braunschweig and supported her marriage to
Gustavus Adolphus of Sweden. Their brother George William did not approve of his sister's marriage because it would jeopardize Brandenburg's status as neutral and antagonizing their Polish neighbours and drag them into the
Thirty Years' War. Anna Sophia´s relationship to Frederick Ulrich having broken down completely, Anna Sophia began a love affair in 1622 with a relative of her husband who lived at the Brunswick court, army officer Francis Albert of Saxen-Lauenburg. The relationship was kept secret for a while, until in 1623, after he had been defeated in a battle at Plesse, his belongings were looted by Anna Sophia's brother-in-law,
Christian of Halberstadt. Christian found several letters from Anna Sophia to her lover talking about her hatred for her husband, her husband's family, and her support for the Catholic side of the conflict in the Thirty Years' War. Anna Sophia, under pretense of a family visit, left Brunswick and returned to her family in Berlin. Well in safety in her native land, she wrote to
Emperor Ferdinand II that her husband had deprived her of "his marital affections and heart", and Georg Wilhelm wrote to his brother-in-law that he should agree to the separation. Instead, Frederick Ulrich had his wife excluded from church prayers and confiscated her assets. However, Anna Sophia did not comply with a summons to Wolfenbüttel before a consistory, and also refused to consent to a divorce and Fredrick Ulric's remarriage. Fredrick died before the divorce was completed. Anna Sophia would later manage to gain control of her dower lands
Schöningen,
Hessen,
Jerxheim, and
Calvörde.
Activities during the Thirty Years' War In order to protect her estates from looting during the wars, Anna Sophia kept up a correspondence with Ferdinand II as well as the imperial commanders
Wallenstein and
Johan t'Serclaes, Count of Tilly. She also negotiated
prisoner of war exchanges on behalf of Brandenburg. == Later life ==