A long-lost musical of Austrian composer Wolfgang Amadeus Mozart has been found at the Czech National Museum in Prague. The score was discovered in the museum's archives, officials said.

"It's a really valuable work long thought to have been lost," the museum spokeswoman Sarka Dockalova told AFP, "It's a joint composition by Mozart and Salieri, a libretto by Lorenzo Da Ponte put to music," she added.

Dockalova said at a press conference that the composition would be "formally introduced" and performed for the first time on 16 February.

The find is particularly remarkable as it was jointly composed by two contemporary composers considered rivals during the classical era – Mozart and Antonio Salieri. Russian poet and novelist Alexander Pushkin is thought to have first highlighted their relationship in his 1832 play, Mozart And Salieri. Moreover, rumours post Mozart's untimely death accused Salieri of poisoning the Austrian composer.

The Italian (Salieri) is to be known jealous for Mozart and the latter had written several letters explaining how his rival attempted to put obstacles while he was performing in Vienna in the 1780s. However, the discovery of the co-authored composition could dismiss the theory that Salieri had anything to do with Mozart's death.

The find coincides with several other events and exhibitions at the museum to mark the 260th birth anniversary and 225th death anniversary of Mozart (1756 to 1791). As part of the celebration, documents, including those written by Mozart, related to his operas in Prague, are on display at the museum.