Complex sentence: The final act provides great irony when Oronte and Enrique arrive on the scene and announce that Horace is to marry Enrique's daughter-which turns out to be Agnès, rendering all of Arnolphe's scheming useless.
Split into simpler sentences: The final act introduces a powerful irony as Oronte and Enrique arrive on the scene and announce that Horace is to marry Enrique's daughter. The daughter turns out to be Agnès, rendering all of Arnolphe's scheming useless.