Auguste von Harrach (30 August 1800 – 5 June 1873), was the second spouse of King Frederick William III of Prussia. Since the marriage was morganatic, she was not named Queen, but was given the titles Princess of Liegnitz (modern-day Legnica) and Countess of Hohenzollern. Frederick reportedly stated, that he did not wish to have another queen after his first one.
Auguste was the issue of Count Ferdinand Joseph von Harrach of Rohrau (1763–1841) and Christiane von Rayski (1767–1830). She met Frederick on a spa in Teplitz in Bohemia in 1822. Auguste and Frederick married at Charlottenburg Palace 9 November 1824. As Auguste was a Catholic and a non-royal, the marriage was initially kept a secret. In many quarters the marriage was greeted with great surprise and some initially refused to believe it. The Princess of Liegnitz converted to Protestantism in 1826.
Auguste was put more or less outside the protocol in the court life of Berlin, she ranked after all the princes and princesses of the royal family. She was not politically active and had no children. She nursed Frederick when he died in 1840, but was not allowed to attend the funeral.
Auguste was given a large allowance and allowed to continue to live in the royal palace as a widow. She made many travels during her later years, to Italy and England. She was the god-mother to her nephew, the painter Ferdinand von Harrach (1832–1915).