The only remaining privately-owned Leonardo da Vinci painting, an ethereal portrait of Jesus Christ, is off to auction.

'Salvator Mundi,' which dates to about 1500, is expected to sell for about $100 million (£75.71 million) at Christie's in November, making it among the most highly-valued works ever to be sold at auction.

'This is truly the Holy Grail of art rediscoveries,' said Alan Wintermute, Christie's senior specialist for Old Master paintings, explaining that the portrait sometimes called the male Mona Lisa had long been thought to have been lost or destroyed.

The portrait depicts Christ in vivid blue and crimson robes holding a crystal orb. 

First recorded in the private collection of King Charles I, the work was auctioned in 1763 before vanishing until 1900, by which time Christ's face and hair had been painted over, which Wintermute said was 'quite common' practise.

Sold at Sotheby's to an American collector in 1958 for 45 pounds, it again sold in 2005 as an overpainted copy of the masterwork, he said.

The new owner started the restoration process, and after some six years of research it was authenticated as da Vinci's more-than 500-year-old masterpiece, which culminated in a high-profile exhibition at London's National Gallery in 2011.

The auction house did not identify the seller, a European private collector who acquired the work after its rediscovery in 2005 and lengthy restoration. The painting stands as the first discovery of a da Vinci painting since 1909.

'Salvator Mundi', or 'Saviour of ther World', will be sold at Christie's in New York at its November 15 sale of post-war and contemporary art following public exhibitions in Hong Kong, London and San Francisco.

'We felt that offering this painting within that context is a testament to the enduring relevance of this picture,' said Loic Gouzer, chairman of Christie's post-war and contemporary art.

Speaking to its $100 million estimate, Wintermute reflected 'There has never been anything like it sold, and so the market will decide.'

The same sale at Christie's will feature Andy Warhol's monumental 'Sixty Last Suppers,' a piece from one of the pop artist's final series before his death in 1987.

The 32-foot, multiple-image work is estimated to fetch $50 million.

Additonal reporting by Reuters.