Georg Nikolaus Nissen wrote to Constanze's sister Sophie, by then married to Jakob Haibel and living in Diakovar, for information regarding Mozart for use in the biography he was writing. Sophie replied to "Monsieur le Chevalier Nissen" on 7th April 1825 and after a message of greeting to her sister and brother-in-law gave a very moving description of the night of Mozart's death - "Now I must tell you about Mozart's last days. - "
