Complex sentence: In 1777, General von Eickstedt became a part of the management of the opera, and it is said that he worked to benefit the career of his mistress Frydendahl, prevented that Caroline Frederikke Müller's lover became employed at the opera, and had him exiled.
Split into simpler sentences: In 1777, General von Eickstedt became a part of the management of the opera, and it is said that he worked to benefit the career of his mistress Frydendahl. He prevented that Caroline Frederikke Müller's lover became employed at the opera, and had him exiled.