Not only is Orlando sane once more, but Rinaldo, having drunk the waters of the contrary fountain, no longer loves Angelica, and willingly promises the hand of his sister Bradamant to the new convert.

But, when brother and prospective bridegroom reach court, they learn Charlemagne has promised Bradamant to a Greek prince, to whom the lady has signified that ere he wins her he must fight a duel with her.

On hearing that the Greek prince is at present besieging Belgrade, Rogero hastens thither, and performs wonders before he falls into the enemy's hands.
But the Greek prince has been so impressed by Rogero's prowess that he promises him freedom if he will only personate him in the dreaded duel with Bradamant.

Rogero immediately consents to fight in the prince's armor, and defeats Bradamant, whom Charlemagne thereupon awards to the Greek prince.
In despair at having forfeited his beloved, Rogero rides off to die of grief, but the Greek prince, riding after him to thank him, not only discovers the cause of Rogero's sorrow, but generously relinquishes all claim to Bradamant and volunteers to witness her marriage to Rogero.

The courage shown by the bridegroom while at Belgrade has meantime so impressed the Bulgarians, that an embassy arrives to beg him to mount their throne.