The portrait's subject was previously unknown

The picture was painted by the German artist Johann Georg Edlinger in 1790, a year before Mozart's death.

The picture was identified as a Mozart portrait when an expert on the composer used computer analysis to compare it with another painted 13 years earlier.

The Gemaeldegalerie says it will go on show on 27 January - Mozart's birthday.

The oil painting, measuring 80cm by 62cm (31.5 inches by 24.5 inches) was acquired by the gallery in 1934 and was only recently restored.

It had been purchased from a Munich art dealer, as a portrait of an unknown subject.

The senior custodian of the art gallery, Dr Rainer Michaelis, recently commissioned extensive computer analysis of the painting and asked Mozart expert Wolfgang Seiller to investigate.

"Mr Seiller noticed there were strong similarities between the subject of the portrait and Mozart," he told Berlin's BZ newspaper.

It is thought the portrait was painted during Mozart's last stay in Munich in 1790. He died of a mysterious illness in 1791 aged 35.