Le duc d'Albe (its original French title) or Il duca d'Alba (its later Italian title) is an opera in three acts originally composed by Gaetano Donizetti in 1839 to a French language libretto by Eugène Scribe and Charles Duveyrier. Its title, which translates as The Duke of Alba, refers to its protagonist Fernando Álvarez de Toledo, 3rd Duke of Alba. The work was intended for performance at the Paris Opéra. However, William Ashbrook notes that "Rosine Stoltz, the director's mistress, disliked her intended role of Hélène and Donizetti put the work aside when it was half completed".

Donizetti then abandoned the score in favour of continuing to work simultaneously on both L'ange de Nisida (later became La favorite), and thus it was nearly 34 years after the composer's death that it was completed by his former pupil Matteo Salvi and received its first performance in an Italian translation and under its Italian title Il duca d'Alba at the Teatro Apollo in Rome on 22 March 1882 with Leone Giraldoni in the title role, Abigaille Bruschi Chiatti as Amelia di Egmont, and Julián Gayarre as Marcello.

It received almost no performances in Italian until the mid-20th century and was only given its first performances in French in May 2012.

The opera had been originally commissioned for the Paris Opéra in 1839, and Donizetti worked on it throughout most of that year. However, he abandoned the project with only the first two acts completed, plus notes for the melodies and bass lines for acts 3 and 4. The opera remained unfinished at the time of his death in 1848.

Although abandoned for the Opéra and still incomplete, Donizetti felt that his contract for this opera had been broken and, in late May 1845, decided to leave Vienna for Paris where he would claim a forfeit from the Opéra for its non-production, which was still unfinished, as was the libretto. He left Vienna for the last time on 10 July 1845, but appears to have done nothing about the claim when he arrived in Paris, and his final illness soon claimed him.

In 1855, Scribe and Duveyrier's libretto was transferred to Verdi's opera Les vêpres siciliennes, with the setting changed from the Spanish occupation of Flanders in 1573 to the French occupation of Sicily in 1282.

In 1881 Matteo Salvi, a former pupil of Donizetti's, completed the opera from Donizetti's notes with the help of Amilcare Ponchielli, Antonio Bazzini and Cesare Domeniceti. Angelo Zanardini translated Scribe's libretto from the original French into Italian. The names of the two lovers 'Henri' and 'Hélène' (which by that time had been used in Les vêpres siciliennes) were changed to 'Marcello' and 'Amelia'.

When Donizetti abandoned the opera, he re-cycled the famous tenor aria, 'Ange si pur' ( 'Spirto gentil' in the Italian version) for his 1840 opera La favorite. For the premiere, Salvi composed a replacement aria, 'Angelo casto e bel'. He also added recitatives and combined acts 3 and 4 into a single final act.