Arriving at the place appointed for the duel, Manuel hears cries of alarm; a page runs to him and says that a Moor has killed Don Carlo. Manuel rushes to Carlo's rescue, meets, fights with, and defeats the Moor...who turns out to be Carlo is disguise. At the same time, Princess Isabella arrives from Portugal, and the court is thrown into disorder when Don Carlo cannot be found. Manuel reveals what has happened; and Duke Mendoza is prominent among the voices that call for Manuel's punishment. But Prince Antonio reveals that the dying Carlo confessed his ruse, and that Manuel though he was rescuing Carlo rather than killing him. More crucially, Piraquo and Pedro reveal the "court secret" — a baby switch: the dead man is actually Mendoza's son Julio, whom Mendoza and his wife, the baby's nurse, had put in Carlo's place when the royal infant was stolen by pirates. (Which means that the false Don Carlo, in pursuing Clara, was courting his own sister.)