Mozart's A major piano sonata K331 manuscript found
1 October 2014 Last updated at 16:21 BST
The head of the Hungarian National Szechenyi Library's music collection has stumbled across a rare discovery.
As he looked through a folder of unidentified music scores, among the many copies and unremarkable scores he suddenly noticed a page that made his heart jump.
The four-page score looked like the original Piano Sonata in A Major, K.331, one of the most well-known sonatas of Wolfgang Amadeus Mozart.
Mikusi cross-checked his finding with Mozart experts, and says they confirmed his discovery.