How many laboratory tests verified da Vinci 's " Lady with an Ermine " ?
In a 2011 exhibition at the National Gallery , London entitled , " Leonardo Da Vinci : Painter at the Court of Milan " ( 9 November 2011 – 5 February 2012 ) , the gallery listed the painting as a possible portrait of Beatrice d'Este , wife of Ludovico Sforza , rather than his mistress , Crivelli .