A rare portrait of Wolfgang Amadeus Mozart – depicting a teenage prodigy in his early prime – has fetched a record price at auction, selling for more than $4.4 million. 

The final amount surprised auction house Christie's, which was anticipating a price between $880,000 and $2.2 million.

What makes the oil-on-canvas piece so sought after is that it is just one of four portraits of the Austrian maestro painted while he was alive.

This particular masterpiece, painted in 1770, also came at a time when Europe was beginning to learn of his musical talents.

Wolfgang Amadeus Mozart had been touring Italy, and captivated the Veronese elite to the extent that his portrait was ordered.

"It's so special, it's so unusual, that I can't compare it to any other picture. So it's once in a lifetime, a portrait of Mozart … that doesn't come every day to the market," said Astrid Centner-D'oultremont, head of the Old Masters' department at Christie's.

The work is attributed to Italian painter Giambettino Cignaroli, but there has been some doubt cast on its origin.

The portrait itself depicts a 13-year-old Mozart playing the harpsichord, in a white wig and red frock.

But what adds an air of mystique to this is the musical score that's featured.

"Some believe it's by Baldassare Galuppi, who was quite a famous composer at the time in Verona, where the painting was painted. And some others believe it's by Mozart himself – and that's quite interesting, because if it is by Mozart, it's one of the first musical scores he ever wrote," said Centner-D'oultremont.

At this stage, the buyer of this artwork remains a mystery, with Christie's only revealing they are a collector from "outside Europe."