Little was known about A Portrait of a Lady and a Boy with Pan by John Hayls, the Baroque painter, when it was aquired by the Tate in 1995.

But a stencilled lot number on the canvas was found to refer to a Christie's sale in 1929, when the artwork - dated 1655-9 - had been described as "Portrait of Mrs Dobson, of West Peckham, Kent, and her son, Thomas Dobson, in a landscape with Satyr and Cupids".

Yet there was nothing cherub-like visible on the canvas. The mystery was resolved when an infrared photograph was taken, which revealed two Cupids holding a wreath, together with a rose in the lady's lap and a theorbo - a long necked lute - at the right of the painting.

Careful cleaning and restoration by Helen Brett, the Tate Paintings Conservator, uncovered the original composition, which is thought to have been overpainted around 70 years ago.

Now the work is to be exhibited at the Tate Britain for the first time since being cleaned and restored...