Simplify the following text for a Grade 8 native English-speaking person.
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: Weber left an opera Die Drei Pintos ( ` The Three Pintos ' ) unfinished . 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 .