• Gaetano Donizetti. Opéra in four acts. 1840.
• Libretto by Alphonse Royer and Gustave Vaëz, with addition by Eugène Scribe.
• First performance at the Paris Opéra on 2nd December 1840.

Fernando, a novice, seeks release from his vows, since he is in love with a woman whose rank and name he does not know. Leonora has him brought to her island home, fearing that he will despise her when he learns that she is the King's mistress. She warns him, as his monastic superior had done, of suffering to come. She gives him a commission in the army, as she leaves to greet the King. In battle he distinguishes himself and is honoured by the King, who remains unaware of the relationship with Leonora. A letter from Fernando to Leonora is intercepted by Don Gaspar, who shows it to the King. He questions her angrily, although the identity of the writer is still unknown to him. Baldassare now appears with a Papal condemnation of the King, bidding him dismiss his mistress and reinstate his wife, the Queen. Reluctantly the King agrees to the command of the Church and when Fernando returns victorious he offers him his own choice of reward. Fernando seeks the hand of Leonora, who now enters, in marriage and this the King generously grants. Fernando, however, is still ignorant of her past and a letter of confession that she sends him never reaches him. After his wedding he is shunned by the courtiers and at last understands that he has married the King's mistress. In distress he casts aside his sword and chain of honour and leaves with Baldassare, intending to return to the monastery. There, as he takes his vows once more, Leonora seeks him out, disguised herself as a novice and explaining how she had tried to tell him of her past. Now he is in love once more, but she dies in his arms, leaving him to pray, with the monks, for her soul.

Fernando sings the praise of his unkown beloved in Una vergine, un'angel di Dio (A virgin, an angel of God). The King's A tanto amor (For such love) is a cynical understanding of how his problems with the Church may be solved, while Leonora's O, mio Fernando (O, my Fernando) expresses her intention of telling her lover of her past. Fernando's moving Spirto gentil (Gentle spirit) marks his returning love for her and before her death she sings Pietoso al par del nume (Merciful like Heaven). The original French version of the opera remains in occasional French repertoire, while abroad the Italian version is generally preferred.