Frederick William III, King of Prussia, A letter from His Majesty the present King of Prussia to his near relative, the reigning Duchess of Coethens, on her departure from the ancient Apostolical faith of the Protestant Church, by her conversion to the new tenets of the Church of Rome, and the doctrines and decrees of Popes and Councils. Translated from a correct copy of the German letter., 1826, Volume: 58. Lord Eldon Manuscript Collection, MSS-056. Manuscripts. https://aspace.ll.georgetown.edu/public/repositories/3/archival_objects/30512 Accessed April 20, 2025.