Complex sentence: Revueltas was a protegé of Carlos Chávez, who had appointed him as assistant conductor of the Symphony Orchestra of Mexico: however, the two men fell out around the time of the commission (and possibly because of it).
Split into simpler sentences: Revueltas was a protegé of Carlos Chávez, who had appointed him as assistant conductor of the Symphony Orchestra of Mexico. However, the two men fell out around the time of the commission (and possibly because of it).