 The two friends also upheld a wast correspondence, which has been partially published.Duchess Charlotte once referred to Sophie Piper as the only true friend she ever owned, and upon the death of Piper in 1816, Charlotte wrote a biography of her.Sophie Piper married the chamberlain count Adolf Ludwig Piper (1750–1795), owner of Ängsö Castle, with whom she had two sons and two daughters, born between 1778 and 1785.