A lost Rubens painting could sell for as much as $7.7 million, or even more, at Sotheby’s next month.

“Saint Sebastian Tended by Two Angels,” was painted over 400 years ago. It shows the young Roman soldier Sebastian, naked and peirced by soldier’s arrows and left to die against an olive tree after he converted to Christianity against the law of the land. Two angels, painted as cherubs, tend his wounds.

Originally commissioned by Ambrogio Spinola around 1606, it belonged to the family for over a century, until it passed in the hands of female descendants. Without the name Spinola still attached, it vanished from history until 1963, when it was sold unattributed in Missouri. In 2008, it went up for auction as a painting by Laurent de la Hyre, a French artist who had been greatly influenced by Rubens. Another painting by the same name by Rubens exists, hanging in the Corsini family collection in Rome, and it was presumed that de la Hyre had copied it in his studies.

This April, the current owner brought his painting for conservation, and in the process it was given x-ray analysis. Details of the underpainting, the layers of paint and gesso beneath the surface, proved this not only to be an original work of Rubens, but the original version of the composition. In short, it is the Corsini version that is a copy, and this the original (though both by Rubens, and neither by de la Hyre).

The X-ray revealed that under the finished version, Rubens tried a few alterations to the posing of Saint Sebastian, and added and omitted various wounds.

“Rubens was one of the most famous, greatest painters of the 17th century,” said George Gordon, co-chairman of oldmaster paintings at Sotheby’s. “and a painter who was really at the forefront of developing the Baroque as an art style.”

The lost Rubens painting will go up for auction in London on July 5 and is estimated to fetch between £4 million and £6 million ($5.1 million and $7.7 million).