A long-lost musical composition by Wolfgang Amadeus Mozart and Antonio Salieri was found tucked away in the collection of the Czech national museum.

“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.

“It’s a really valuable work […] long thought to have been lost,” said Ms Dockalova.

Salieri 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, as the Independent writes.

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, because he was jealous of Mozart’s genius are partially due to Alexander Pushkin’s 19th century poetic drama “Mozart and Salieri”.