The way JMW Turner depicted a storm at sea shocked his contemporaries, and foreshadowed the evolution of abstract art.

The painting, signed Turner, depicts the castle overlooking the River Wye, showing the view from downstream of a wooden bridge, complete with a boat in the foreground, alongside a series of cottages.

But after the buyer, who wishes to remain anonymous, discovered a hidden inscription of 'W Turner' on the back of the painting, experts managed to confirm its artistry. It is now expected to sell ...