“When the dusty heirlooms and bric-a-brac of a once-stately French family went under the hammer at a minor auction eight years ago, an anonymous portrait of the Dutch scholar Erasmus sold for €2000… [now] experts have established that the work was the last ever portrait that Holbein painted of an ageing Erasmus, and the painting – one of a tiny minority of Holbein works to be in private hands – is worth millions.”