'Lost' Holbein set to fetch £3m (original estimate: £3,000)

When this portrait was last sold in 1974, it was grubby, and over-painted, with the artist identified only as British. It went for less than £3,000.

But this year it was confirmed as being a portrait by the German painter Hans Holbein of the wayward son of a prominent courtier of Henry VIII. It is set to make up to £3m at auction at Sotheby's in London on 5 July.

The rediscovery of the portrait, thanks to detective work by Sir Roy Strong, the former head of the Victoria and Albert Museum, whose suspicions were first raised 30 years ago, means it will be the first Holbein to go to auction. The work is thought to be the last from Holbein's time in England to remain in private hands and was completed just two years before his death in 1543.

It was probably commissioned by Thomas Wyatt the Elder, treasurer to Henry VIII, probable lover of Anne Boleyn, poet and classical scholar, and the first to translate Petrarch into English. One of his most treasured possessions was a cameo ring bearing a portrait profile of Julius Caesar.

In having his son painted in a classical manner, in a composition unique in Holbein's work, Wyatt may have been trying to have his unruly son portrayed in a manner to which the subject might aspire. If so, he failed. Wyatt the Younger was beheaded for treason after leading a rebellion against the marriage of Mary Queen of Scots and Philip of Spain. Even before this, he had been confined to the Tower of London for eating meat on Fridays and fast days.

George Gordon, of Sotheby's Old Master paintings department, said the composition was very unusual for the date in England but reflected the interest in Renaissance styles and ideas from the Continent that Henry VIII was seeking to introduce to his English court. But despite its novelty, the portrait's history becomes untraceable after Thomas the Younger was beheaded in 1554.

"The possessions of the family seem to have been dispersed when Thomas Wyatt the Younger had his head cut off," Mr Gordon said. "It vanished as far as we [today] are concerned."

When it eventually turned up for auction in 1974, it had been substantially over-painted and did not look like a Holbein. Only after subsequent cleaning and further research was it identified.