The recent discovery during cleaning of the initials 'AJ' in the bottom left corner of 'El Coloso' proved decisive in concluding that the work previously attributed to Francisco de Goya, was, in fact, painted by his only known apprentice, Asensio Juliá.

Found just a few weeks ago by José Luis Díez, who is head of the 19th century painting conservation department, it was the final clue sought by a team of Prado Museum experts that has been investigating the painting's authorship since 1991.

'El Coloso', which was painted between 1808-1812, will be taken out of the Goya catalogue, but will remain on show at the museum.

The revelation will prompt further research into the life and work of Asensio Juliá, about whom very little is known.