HIS death was the stuff of legend: stabbed in the back as he valiantly tried to stop his men from firing on the islanders of Hawaii.

But for 225 years, it seems our perceptions of the glorious demise of Teesside-born Captain James Cook may owe more to 18th Century spin than reality.

A previously unrecorded watercolour was unveiled yesterday and it focuses renewed attention on the long-disputed final moments of the North-East navigator and explorer.

It depicts Cook not nobly protecting life, but in hand-to-hand combat, fighting with natives after going ashore at Kealakekua Bay on February 14, 1779, to investigate the theft of one of his boats by an islander.

The unedited picture was painted by Deptford artist John Cleveley from first- hand accounts made by his brother, James, who was a carpenter on the Resolution during Cook's third, fateful voyage.

The watercolour was among a collection that formed the models for a famous set of aquatints, the work of engraver Francis Jukes and published by Thomas Martyn, in 1788.

Advertised as "scarcely to be distinguished from the original drawings", the prints followed John Cleveley's work closely - with the remarkable exception of Cook's death.

The artist's depiction of Cook fighting for his life on the beach, in the right foreground, has been replaced by the dramatic moment of his death.

The substituted version shows Cook, not in hand-to-hand combat, but turned away from his assailants, signalling to his ships to cease fire, as an Hawaiian chief prepares to stab the navigator in the back of the neck.

This glorified image of Cook as noble hero was famously depicted in John Webber's drawing Death of Captain Cook, first engraved in 1782, and, subsequently, in a painting by Francesco Bartolozzi and William Byrne.

By the time Martyn published the plates in 1788, John Cleveley had been dead for two years and this may have become the "authorised" version of Cook's death, showing him as dying heroically, a victim of his humanity.

"It was, perhaps, enough, to persuade him to alter Cleveley's representation," said Christie's specialist Nicholas Lambourn at yesterday's unveiling.

"With the artist dead, one assumes the engraver was charged to alter the scene."

The set of four original Cleveley watercolours, which have passed down through the family of Quaker philanthropist Ann Hopkins Smith, of Olney, Buckinghamshire, who died in 1851, are expected to fetch up to £150,000 when auctioned at Christie's, in London, on September 23.

Capt Cook was born in Marton, part of Middlesbrough, in 1728.

The exact chain of events surrounding his death are still hotly debated but scholars have concluded that he acted with uncharacteristic rashness and provocation to the islanders of Hawaii. He was also betrayed by panic and inefficiency among the armed marines whose job it was to protect him.

At the same sale, a pocket hammer carried by Capt Cook is expected to fetch up to £30,000. The rare personal relic was presented to his friend and patron, Sir George Jackson, second secretary to the Admiralty, judge advocate of the Fleet and for whom Capt Cook named Port Jackson - modern-day Sydney Harbour.

* In his three voyages of discovery, Cook did more than any other navigator to add to our knowledge of the Pacific and the Southern Ocean.