Anonymous painting bought at auction on ‘hunch’ identified as two-in-one Rubens

Study of man often featured in works by the Flemish master reveals hidden painting of woman beneath model's beard

Is it a bald elderly man with a big bushy beard and a wine-addled stare? Or a friendly young woman with flowing locks and a crown of braids?

To Belgian art dealer Klaas Muller, an answer to that question mattered less than the fact that this particular take on the duck-rabbit optical illusion was painted by one Peter Paul Rubens.