The collaborative effort, a libretto, between Antonio Salieri and Mozart was found tucked away in the reserve collection of the Czech national museum, according to The Local.
“It’s a joint composition by Mozart and Salieri, a libretto by Lorenzo Da Ponte put to music,” Sarka Dockalova, the museum’s spokeswoman, told AFP.
Salieri, a key figure in the development of late 18th-century opera, was described by Mozart in various letters as a “favourite” Italian composer of the Emperor of the time, Joseph II, and his rival in musical terms.
“It’s a really valuable work […] long thought to have been lost,” said Ms Dockalova.
According to letters sent to his father, Mozart said “the only one who counts in [the Emperor’s] eyes is Salieri.”
Rumours circulated after Mozart’s early death in 1791 that Salieri had poisoned the Austrian composer, which were further compounded by a 1984 film of his life, “Amadeus”.
The discovery of a co-authored composition would appear to support the long-since dismissed theory that Salieri might have played a role in Mozart’s death.