Rosimonda, whose fate might have been dire but for her successful rescue by Faramondo's men, returns to her father's court, with news that the treacherous Gernando has been captured. But she is in time only to see her father lead Faramondo to the altar in preparation for the blood-oath sacrifice. Disaster lies upon Faramondo – one stroke of the weapon, and he will lie dead... but for the sudden news brought by a messenger direct from Teobaldo. In the letter, Teobaldo (who lies dying of many wounds incurred in Sarmazia) admits that he had not turned suddenly against Gustavo, but rather that his desire to oust Gustavo of his position had been long in the planning. He had in fact switched infants when the king's son was born; in other words, Sveno was NOT the king's son... but Teobaldo's. It slowly sinks in to all present that, since Sveno was not Gustavo's son, Gustavo does not need to kill Faramondo. All ends happily with general rejoicing; Gustavo and Faramondo cry friends, Gernando is released and realises only too late what an ally he had lost in the noble Faramondo, Clotilde and Adolfo are united, and so too are Rosimonda and Faramondo.