Complex sentence: Beauséant persuades Melnotte to disguise himself as a foreign prince but when Melnotte takes Pauline to his widowed mother's home after the marriage, she learns the truth and the marriage is annulled.
Split into simpler sentences: Beauséant persuades Melnotte to disguise himself as a foreign prince. When Melnotte takes Pauline to his widowed mother's home after the marriage, she learns the truth, and the marriage is annulled.