The 19th century Hungarian composer, Franz Liszt, was prolific and won a feverish fan base, but he was best known for his piano pieces and only premiered one opera, a one-act work the prodigy completed when he was 13.
"Sardanapale," based on Lord Byron's tragedy "Sardanapalo" about the overthrow of a peace-loving but hedonistic Assyrian king, was long thought to have been abandoned.
David Trippett, a senior lecturer at Cambridge University, said he discovered the manuscript in an archive in Weimar, Liszt's longtime base in Germany, and spent two years restoring it.
"We will never know exactly why he abandoned his work on the opera and I suspect he would have been surprised to learn that it is resurfacing in the 21st century. But I like to think he would have smiled on it," Trippett said in a statement.
Trippett called the opera -- which Liszt began in 1849 and is in Italian -- groundbreaking as it blended Liszt's characteristic voice with the composer's newfound discovery of Richard Wagner, his contemporary and one of the defining figures in opera.
"The music that survives is breathtaking -- a unique blend of Italianate lyricism and harmonic innovation," Trippett said.
Only one act of "Sardanapale" survives and Trippett said that it was at first barely legible, with Liszt writing in a shorthand that only he understood.
But Trippett said he was able to recreate the piece as it was clear that Liszt "worked out all the music in his head before he put pen to paper."
"To retrieve this music, I've had to try and put myself into the mind of a 19th century composer, a rare challenge and a remarkable opportunity," he said.
The scholar plans to premiere "Sardanapale" in June at the BBC Cardiff Singer of the World competition, a leading annual event in Wales for aspiring opera singers.
"Who else gets to premiere a new opera by a superstar composer from two centuries ago?" said the Armenian soprano Anush Hovhannisyan, who is taking part in a documentary on the restoration timed for the Cardiff event.
Until the re-emergence of "Sardanapale," Liszt was only known in opera for "Don Sanche, ou Le Chateau de l'Amour" ("Don Sanche, or the Castle of Love"), a French-language one-act piece from 1825 that fell into obscurity for decades.