Anna Constantia von Brockdorff (17 October 1680 – 31 March 1765), later the Countess of Cosel, was a German noblewoman and mistress of Augustus the Strong, King of Poland and Elector of Saxony. Eventually he turned against her and exiled her to Saxony, where she died after 49 years of imprisonment.Anna Constantia was born in Gut Depenau, today part of Stolpe, Holstein, the daughter of the Knight (Ritter) Joachim von Brockdorff and his wife Anna Margarethe, daughter of the rich Hamburg citizen Leonhard Marselis, owner of Gut Depenauborn.