Did Leonardo da Vinci paint a nude Mona Lisa? I may have just solved this centuries-old mystery

It is one of the most tantalising – and entertaining – puzzles in art, stretching from the Louvre to the Loire via, well, Norfolk. And our critic thinks he has just worked it outIncreased security after the recent heist has made the queues at the Louvre even slower, yet on this rainswept, very wintry morning, no one grumbles. After all, the Mona Lisa is waiting inside for all these tourists who have come from the world over. Leonardo da Vinci’s woman – swathed in dark clo