'James Wyatt and his Granddaughter Mary Wyatt' was a copy of a John Everett Millais painting by his brother William
A copy of a painting by Pre-Raphaelite artist Sir John Everett Millais could fetch up to £30,000 at auction.
'James Wyatt and his Granddaughter Mary Wyatt' was painted in 1850 by his lesser known brother, William Henry Millais.
An accompanying letter, which will be sold with the painting, confirms that Sir John finished the faces and hands in the picture.
He also acted as agent, confirming the commission for James Wyatt's son.
"The original painting was commissioned by James Wyatt from Millais in 1849," explains Charles O'Brien, Department Head of 19th Century Paintings at Bonhams.
"He was a great fan and one of his patrons. He'd been Mayor of Oxford in the early 1840s and had a number of works by Millais.
"The original picture then went into the possession of James Wyatt's godson and it then appeared at auction."
The original work is now in the personal collection of Sir Andrew Lloyd Webber.
"The copy came about as a gift from James Wyatt Jr to his brother George," Charles O'Brien continues.
"George was extremely fond of the Millais portrait of his father, and James Wyatt Jr therefore decided it would be a good idea to have William Henry Millais - ie. Sir John Everett Millais' brother - to paint a replica of the portrait which he then gifted to his brother George."
Sir John gave the painting his seal of approval. In his letter to James Wyatt Jr he wrote: "William has completed the copy of your father and I think it cannot help serving your perfect satisfaction. I've looked over him and just touched the faces a little.
"Your brother George I think would like it above all presents in the world."
William Henry Millais was predominantly a landscape painter and was largely overshadowed by his famous brother.
"His output wasn't enormous," Charles O'Brien explains. "While his paintings have been competent they're not particularly outstanding.
"So this is extraordinary because of the sheer quality of the work. One might assume that Sir John Everett Millais worked on a little bit more of it than he'd admitted to."
With the brothers working together to create the replica there is little evidence of a sibling rivalry or jealousy on William's part.
"The tone of the letter would suggest they were very fond of each other and that William was very happy that his brother helped him with the painting."
James Wyatt was an art collector and dealer who lived in Oxford and was once the curator of the Duke of Marlborough's collection at Blenheim.
He was also a wood carver and set up his business on the High Street. He lived above the shop with James Wyatt Jr.
It was a popular haunt of the Pre-Raphaelites and John Millais stayed with them on one occasion and painted the picture.
"Not only does it offer us a completely new insight into the quality of the work of William Henry Millais, it's also an interesting example of how the two brothers cooperated on a painting together," says Charles O'Brien of the picture.
"I think it shows a rather nice and touching filial approach into making a version of the original portrait.
"The painting itself is the most beautiful, stunning picture."
William's brother Sir John Everett Millais was one of the founders of the Pre-Raphaelite Brotherhood. His paintings have become some of the best known images from the mid-19th century.
His painting of Shakespeare's Ophelia has recently been estimated to be worth £30 million.