It’s a double whammee. When this picture was acquired in London by some sharp-sighted collector it was a portrait of an unknown person painted by an un-identified artist. Now it would seem that this artist is the painter Dosso Dossi who, if not as famous as such high Renaissance contemporaries as Michelangelo and Titian, knew how to adapt their discoveries with a remarkable facility to his often fanciful compositions and so made his services much coveted at the court of Ferrara which was a leading centre of late 16th century Italian art.

And then, on top of that, it turns out to be a portrait of the woman who married a prince of the region: and who happens to be one of history’s most famous femme fatales to boot. What could be better? Well, only the fact that no other portraits of her are known to exist.

Across the centuries artists have fantasised over this enigmatic villainess: from Bartolomeo Venetzino who paints her with tumbling blonde locks to Dante Gabriel Rosetti who prefers to imagine her as a golden-haired temptress and depicts her washing her hands after preparing her famous poison draft. Now, if the identification is correct (and judging by the tell-tale dagger – the one she supposedly plunged into her chest after being raped by the son of the King of Rome - it could well be), it turns out that this cold blooded murderess of our much loved myths was, rather more probably, a brunette seductress – though with perhaps a hint of henna there, because it was fashionable at the time.

And does it matter? It’s still the same painting we are looking at.

Of course it does. And its not just about value – though of course that has gone up. When we stand before a portrait, we respond to it, instinctively, as we would a real person. And it’s perfectly natural – if not particularly laudable – that we look at a celebrity more attentively.

Now we want to see if her story is written on her features. We want to see whether evil creeps into a face. The woman in this portrait certainly looks pretty sinister, her sidelong face half in shadow, her eyes feline. What is she plotting her contemporaries must have wondered? Then she stared at them with the inscrutably narrowed gaze of a powerful aristocrat. Now, with the advantage of posterity, we think we know.

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