El Coloso, the famous painting of a naked giant striding past a caravan of terrified people — supposedly an allegory of the brutal Napoleonic war in Spain — is not by Francesco de Goya, a Prado museum specialist says. After some 20 years of study, the Prado’s senior Goya specialist determined the painting was by one of his pupils — presenting a problem for the Madrid museum, where the painting has held pride of place and where a blockbuster Goya retrospective opened in April