Eight years of detective work will culminate in July’s first performance of ‘amazing’ tragedy by great Italian composer

A lost opera by one of the great Italian composers is to have its world premiere in London almost 180 years after it was written.

Gaetano Donizetti was a leading figure in 19th-century Italian music, along with Giuseppe Verdi and Vincenzo Bellini. His most famous work, Lucia di Lammermoor, written in 1835, is seen as one of the great European operas. But L’Ange de Nisida (The Angel of Nisida) – composed in the late 1830s after he moved to work in Paris – never saw the light of day. It was written for the city’s Théâtre de la Renaissance, but the company went bankrupt before it was premiered.

The opera was thought to have been lost until musicologist Dr Candida Mantica, then a PhD student at Southampton University, painstakingly located and deciphered the score’s fragments over eight years.

Mantica said she found some pages in Paris’s Bibliothèque Nationale, but they were scattered among 18 folders and in no specific order. The reconstruction involved archive research across Europe and the US. “I was able to identify about 470 pages of autograph music [in the composer’s hand] thanks to a draft copy of the libretto, which allowed me to establish their original order,” she added.

The work will be premiered on 18 July at Covent Garden by London-based Opera Rara, which performs and records rare and forgotten 19th-century operas, in partnership with the Royal Opera House.

L’Ange de Nisida is a romance, telling the story of a soldier, Leone, who is in love with his king’s mistress.

Facebook Twitter Pinterest Gaetano Donizetti in a portrait by Gennaro Ruo. Photograph: Getty

Sir Mark Elder, artistic director of Opera Rara and music director of the Hallé Orchestra, will conduct the performance. He told the Observer: “It’s a work of top quality. Very beautiful.” Donizetti used some of this music in later works, including 1840’s La Favorite, but Elder said: “Over half of [L’Ange] has never ever been heard, which is terribly exciting.”

He said it had some “very powerful scenes” and noted that, because it was designed for a smaller theatre, “there is a delicacy and intimacy about the writing that is gorgeous”.

Donizetti died in 1848, aged just 50, and his masterpieces also include the 1832 comedy L’Elisir d’Amore (The Elixir of Love).

Roger Parker, repertoire consultant to Opera Rara and music professor at King’s College, London, said: “For L’Ange to get as popular as Lucia di Lammermoor or L’Elisir d’Amore, that would be ambitious. Who knows what’s going to happen? But the musical quality is as good as anything he did. That’s the surprising thing about it. When operas are discovered, quite often you find they were undiscovered for good reason. But this one really is amazing music. It’s some of the best music that you’ll hear from Donizetti.”

He added: “All his other operas have been premiered now. This is the last one, and it’s one of the best.”

Donizetti’s letters of the period reflect his annoyance over his cancelled opera, and despair over the commissioning theatre company. In one he complains that: “The management were real donkeys.”

Parker believes that L’Ange de Nisida will “rewrite how we think about [Donizetti] as a composer, in particular about the breadth of his musical inspiration. It’s a curious mixture of the comic and the serious.”

Donizetti scholars knew of this opera, he said. “But they had no idea what it was like … So there was no discussion of it in any of the literature.”

He praised Mantica’s “astonishing” detective work: “Candida just went to Paris and kept finding another few bars. I think we’ve got more or less everything he wrote now.”

The opera is likely to last about two-and-a-half hours, excluding the interval. The soloists will include soprano Joyce El-Khoury as Sylvia. A live recording will be made for release next year. The premiere will be a concert performance rather than a full staging. Covent Garden is “a wonderful platform for bringing this unknown piece to people’s attention”, according to Elder. “I can imagine it being staged, absolutely.”