Musicians this weekend will for the first time publicly interpret music for flute and harp that Wolfgang Amadeus Mozart wrote as a 22-year-old while teaching an aristocratic French student.
The unprecedented concert on Sunday at France's National Library (BnF) comes after what it has called a "major discovery."
Francois-Pierre Goy, a curator in the library's music department, stumbled across the treasure as he examined a pile of anonymous manuscripts he wanted to get through before retirement.
"I never imagined what I was about to find," he told Agence France-Presse (AFP).
The 44-page notebook includes a dozen daily exercises the Austrian prodigy gave Marie-Louise-Philippine de Bonnieres de Guines from May to July 1778, as well as seven pieces for flute and harp, he said.
She was an excellent harpist and the daughter of the Duke of Guines, himself a renowned flutist.
"It just so happened that I had been looking at some of Mozart's teaching material a few weeks earlier," Goy said.
Soon he noticed similarities, including "the treble clefs that are quite rounded and tilted slightly forward," and the bass clefs drawn in the opposite direction from how they usually are in France, he added.
"Could it be him?" Goy said he thought to himself.
Comparisons with Mozart's other handwritten works, the French paper used and stamps on the notebook identical to those on a French copy of Mozart's "Concerto for Flute and Harp" that the Duke of Guines had commissioned all seemed to indicate he was right.
Armin Brinzing, director of the Austria-based Mozarteum Foundation, authenticated the document in April.
The manuscript "is part of two bundles of music that were confiscated from the home of the Duke of Guines in 1794" during the French Revolution and eventually ended up at the BnF, according to the library.
Mozart died in 1791, aged 35.
Discoveries like this, "for such a famous composer are almost unheard of," said Mathias Auclair, director of the BnF's music department.
Several Mozart compositions have been rediscovered in recent years.
In one case, in 2012, someone found a Mozart piano piece composed when he was 11 in an Austrian attic.
For harpists and flautists, who have "very little repertoire" available to them, the discovery at the BnF is a wonderful surprise, he said.
BnF president Gilles Pecout said the new music sheets shed light on Mozart as a young teacher and documented his last stay in Paris in 1778, on which there is scant information.
