The BBC has proven that Lucian Freud did in fact produce a portrait he denied painting for years.

The work dates to 1939, while Freud was studying at the East Anglian School of Painting.

Freud painted the work circa 1939, while studying in Essex

It's not up to Freud's usual standards, which may explain his repeated insistence that someone else was behind it.

However, detailed testing by the BBC for the programme Fake or Fortune has revealed that it was the work of a single artist - identified as Freud himself.

The origins of the painting remain mysterious.

Somehow it ended up in the hands of Peter Werth-Miller, a fellow artist who had studied with Freud and had disliked him for many years.

Werth-Miller gave the painting to a friend, an illustrator named Jon Miller, suggesting he sell it publicly in order to embarrass Freud.

However, when the painting was sent to be valued at Christie's in 1985, the auction house was convinced by Freud's insistence he'd had nothing to do with it.

The work has since been valued somewhere in excess of £300,000 ($396,882).

The BBC's Fiona Bruce explained: "As this investigation progressed we had to investigate Freud the man as much as the painting. He was an extraordinary and controversial character.

"And only by understanding him could we begin to understand why he would deny that a painting of his was in fact by him."

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