An important painting by George Stubbs, commonly regarded as the master of equestrian art, is set to be auctioned for around £400,000 this summer.

A dark bay thoroughbred in a landscape is expected to fetch £400,000-600,000 when it goes under the hammer on Wednesday 9 July in Bonhams’ Old Master Paintings Sale, to be held at 101 New Bond Street.

The painting, which had been thought lost since the 1950s, was rediscovered by Bonhams’ during a recent probate valuation.

Bonhams’ says the oil on canvas (127 x 101.5cm) is in exceptionally good condition, unlike many of Stubbs’ oils on panel, which have not fared as well.

According to the auction house, little is known of the painting’s early history, although it is thought to date from the early 1760s, and is presumed to have been an important commission, due to its impressive size.

A century later, the canvas was hanging in one the UK’s grandest houses, Blenheim Palace in Oxfordshire – home to the Dukes of Marlborough. The 8th Duke of Marlborough is thought to have sold it in 1886, along with a number of other works of art.

George Stubbs’ first love was anatomy and his precise dissections were recorded in detail. His Anatomy of the Horse was publishedin 1776 and this knowledge was then translated into his incredible works of art.

Bonhams’ Old Master paintings specialist, Andrew McKenzie says: “This painting offers the world’s collectors, museums and institutions the rare chance of acquiring a classic image of British Art and we foresee fierce competition.”