Original: His unfinished opera Die drei Pintos ('The Three Pintos') was originally given by Weber's widow to Meyerbeer for completion; it was eventually completed by Gustav Mahler, who conducted the first performance in this form in Leipzig on 20 January 1888.
Simplified: Meyerbeer was going to finish it, but in the end it was Gustav Mahler who finished it and conducted the first performance of the completed work in Leipzig in 1888.