SHE WAS a poorly educated but stunning model, married to the leading Arts and Crafts designer of his day. And, like many a model before and since, she had an affair with the artist.

William Morris was besotted with Jane Burden from the moment he was introduced to her by their mutual friend, the painter Dante Gabriel Rossetti.

She was 18, he 25. Now, in the house where they spent the first five years of their marriage, a mural celebrating their love has been discovered after lying hidden behind panelling for 140 years.

The find at the Red House in Bexleyheath, southeast London, which Morris had built for his marriage to Jane in 1860, has excited the property’s present owners, the National Trust. But they do not know who painted it; was it Morris, or one of his circle in the Pre-Raphaelite Brotherhood?

It might have been Rossetti, who painted Jane on many occasions and with whom he subsequently had a torrid liaison.

“This is a remarkable find because the painting has been hidden from view for so long,” Robert Quarm, curator of the Red House, said yesterday.

“Morris was very much in love with Jane at the time of these paintings, which were done a long time before the affair. We always wondered if something like this lay behind the panelling, as the house was the centre of an artistic community, and they put much of their energies into decorating it.”

The mural, in glowing, earthy colours, bears the French proverb Qui bien aime, tard oublie (He who loves truly, forgets not easily), a quotation from Chaucer’s Parliament of Fowles. The 14th-century author of The Canterbury Tales was a major influence on Morris. It is tempting to think that Morris, who was devastated to discover that his wife was sleeping with his best friend, covered up the mural in a fit of jealous rage.

The more prosaic truth, however, is that the panelling was erected by a subsequent owner who clearly thought it was not the best example of Pre-Raphaelite art in the house, which has other, better, wall paintings by Rosetti and Edward Burne-Jones.

Someone else appeared to share that view. Part of the original mural has been painted over by a subsequent work that appears to be some kind of Chaucerian allegory. Conservators are considering removing it in the hope of finding more of the original underneath.

The trust plans to raise £20,000 to fund research into other rooms in the house in case more hidden treasures from the couple’s five-year residence are waiting to be unearthed. Rosetti described the Red House as “more a poem than a house, but an admirable place to live in”.

Morris was painting murals for the Oxford Union when he first met Jane, the near-illiterate daughter of a local stableman. He was obsessed with her from the first, to the extent that he could not bring himself to depict her on canvas. “I cannot paint you, but I love you,” he once told her. Morris set about educating her privately. She became so sophisticated, queenly even — and a talented embroiderer in her own right — that Bernard Shaw based Eliza Doolittle in Pygmalion on her.

Impending marriage spurred Morris to build the Red House, an Arts and Crafts gem designed by his architect friend Philip Webb. In 1904 a German critic described it as “the first house to be conceived as a whole inside and out, the very first example in the history of the modern house”.

Morris and Jane had two daughters before moving to Kelmscott, in Oxfordshire, the house most associated with the designer whose wallpaper and fabric patterns are still hugely popular today. It was then that the affair with Rosetti began.

Morris had a successful interior design business in London, but he was so tormented by his wife’s infidelity that he travelled to Iceland to bury himself in writing poetry and translating Norse sagas. The couple never divorced. Morris died in 1896; Jane outlived him by 18 years, and was still being drawn by artists in her later years.

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