Dido Belle: the artworld enigma who inspired a movie

The enigma of Mona Lisa's smile? Who cares? The mystery of Dido Belle is much more intriguing. The double portrait Dido Elizabeth Belle and Lady Elizabeth Murray, once attributed to Johann Zoffany and now hanging in Scone Palace in Perth, depicts two elegant 18th-century women in silks and pearls at Kenwood House in London. Beyond them, you can just glimpse St Paul's and the rest of the Georgian cityscape. Nothing unusual about any of that, but for one detail – Dido is mixed race.

The first question that strikes the viewer is: why is Dido pointing at her cheek? It is a "puzzling gesture", wrote English literature lecturer Christine Kenyon Jones, in an article for the Jane Austen Society of North America. "Is it meant to draw attention to her skin colour, or simply to her smile and her dimples?" Might it even be, as a new theory suggests, an allusion to the Hindu deity Krishna?

These questions – and the mystery of what she was doing, both at Kenwood and in the painting – feel especially topical since Dido, the daughter of a former slave and a British aristocrat, is now the subject of a film, Belle. Meanwhile, a new biography of her great uncle and benefactor Lord Mansfield sheds more light on her 30 years at Kenwood. The painting has even inspired a novel. "The reason it struck me," says Caitlin Davies, author of Family Likeness, "was that I grew up near Kenwood, so had been in and out of the house for 45 years. Then suddenly, in 2007, I saw this portrait when it was on temporary display, in an exhibition, Slavery and Justice."