Celebrated artist Lucian Freud is thought to have denied painting what might be one of his first ever works because of a bitter feud with a rival artist, a BBC investigation suggests.

On Sunday night’s episode of Fake or Fortune?, art detectives will explore the possibility that Freud rejected the attribution of ‘The Man in the Black Cravat’ to prevent one of his greatest enemies from earning a fortune from its sale. For decades, artist Denis Wirth-Miller attempted to sell the portrait without success. At first, auction houses and experts considered it to be a genuine work possibly painted in 1939 while Freud was at art school. However, they changed their mind soon after speaking with Freud. Were it not for Freud’s interference, it is believed the painting could have sold for as much as £500,000.

Wirth-Miller and his boyfriend, Richard “Dickie” Chopping are thought to have discovered the work during WWII in one of the barns at the East Anglian School of Painting and Drawing or a nearby junk shop. Freud trained alongside Wirth-Miller at the art school in the early 1940s where they developed a rancorous though unexplained feud. Wirth-Miller would write lists under the title “Reasons I hate Lucian Freud”. For his part, Freud referred to his enemy as “Worst Miller”. Before his death in 2001, Wirth-Miller left the painting to art expert Jon Lys Turner with an express instruction: “I want you to sell this picture as publicly as possible. I want you to humiliate Lucian Freud.”

Determined to carry out Wirth-Miller’s wishes, Turner approached Freud’s daughter, Rose Boyt, to confirm the attribution but his investigation was similarly thwarted. Boyt refused to question her father knowing the interrogation would rankle him. “If he hadn’t identified it in the normal course of things, that meant he didn’t want to because it was stolen, it wasn’t by him or he hated it,” she told the BBC. Puzzled by Freud’s obstinance, Turner soon realised the artist was still nursing the old grudge. He has vowed to fulfil his promise to Wirth-Miller and sell the painting if the attribution is verified.

Fake or Fortune? airs on BBC One on Sunday (17 July).