He would probably be surprised to read it, were he alive to do so, but the best known Mayor of Oxford ever to walk behind the mace was probably James Wyatt (1774-1853). He lived above his shop at 115 High Street from 1805 until his death, and his children continued to live there for another 30 years or so.

James Wyatt was the fourth son of a baker. He was Mayor of Oxford in 1842-3 (not Lord Mayor; the Lord bit was added to the job description in 1963) and a portrait of him hangs in the Town Hall — which is remarkable not because of the painting itself ,but because of its gilded frame which incorporates the tools of his trade: those of a wood carver, gilder, and picture framer.

He is famous these days for the paintings of him and his family by Millais. Now auctioneers Bonhams plan to sell a picture of him by William Millais (1828-1899) later this year on behalf of Wyatt’s descendants.

William Millais? I hear you ask. Yes, because the painting going under the hammer in London on September 29, and expected to fetch between £20,000 and £30,000, is a copy of one entitled James Wyatt and his Granddaughter Mary Wyatt by the much more famous Sir John Everett Millais (1829-1896), brother of William, and of course a founder member of the Pre-Raphaelite Brotherhood, now in the collection of Lord Lloyd-Webber.

After the death of James Wyatt — and by coincidence his will was proved on September 29, 1853 — it seems that his family, who lived with him at 115 High Street, commissioned the painting by William, the amiable brother — who was one year older than John but never jealous of him — as a memento.

Wyatt, who by 1849, when the original was painted, had set himself up as an art dealer as well as a frame maker, was one of John Everett Millais’ first patrons. Indeed John, or Jack as he was known, used often to stay at 115 High Street.

The Millais brothers spent their early childhood in their native Jersey, but their parents, spotting John’s prodigious talent for drawing, moved to London so that he could attend the Royal Academy where he became, at 11 years old, the youngest student ever to be accepted.

On the wall behind James Wyatt in the painting is a picture of his daughter-in-law Eliza, also destined to sit for a portrait by John Everett Millais. On the table in front of him is one of his treasured possessions, an oak box carved by himself, which is now also up for sale along with the painting and a letter concerning it from John.

The teenaged Jack Millais, met Wyatt and indeed Thomas Combe, printer to the University — whom he also painted — while staying with his half-brother, Henry Hodgkinson, in Oxford. Wyatt, who in time became the curator of paintings at Blenheim Palace, obviously had a good eye for up-and-coming artists. He even displayed J. M. W. Turner’s famous picture of Oxford High Street at his shop — thus dealing with the two most famous British artists of his time.

The painting now coming to auction will excite many connoisseurs of Pre-Raphaelites, not least because it turns out that much of it was indeed painted by the more famous brother. Bonhams expert Charles O’Brien says that it is known that Wyatt’s face was painted by John and he says that “on closer inspection his hand is evident throughout the painting”.

He adds: “It’s a beautiful picture suffused with the light of summer, made more wonderful by the hidden message of brotherly love.”