It almost sounded too good to be true: a Picasso painting stolen in one of the world’s most famous art heists had been found under a tree in a snowy Romanian forest.

On Monday it emerged it was totally too good to be true, part of an elaborate and carefully staged piece of performance art by a radical Belgian theatre company.

Picasso’s 1971 Tete d’Arlequin (Harlequin’s Head) was stolen from the Kunsthal gallery in Rotterdam six years ago in what has gone down as one of the most remarkable art heists of modern times. It was one of seven paintings, along with a Monet, Gauguin, Matisse and Lucian Freud, taken with startling speed and ease in the dead of night.

Two Romanian men, Radu Dogaru and Eugen Darie, were jailed by a court in Bucharest in 2013 after admitting their part in the thefts. Security, the ringleader said, had been “practically non-existent” and he entered “just with a screwdriver.” They smuggled the paintings in to Romania in pillowcases before trying, and failing, to sell them on.

Dogaru’s mother Olga initially said she burned the paintings to help her son but then changed her story. Museum experts, however, said they found ash in her kitchen stove which contained the remains of three oil paintings and nails from 19th century frames.

The Dutch writer Mira Feticu wrote a novel about the heist and it was she, along with journalist Frank Westerman, who discovered the Picasso painting in a forest in eastern Romania after being sent an anonymous letter with instructions on where it was hidden. They found it wrapped in plastic, under a rock at the foot of a tree.

The picture was handed to the Dutch embassy in Bucharest and was about to be properly examined by experts. On Sunday Feticu received an email telling her it was in fact a hoax.

The perpetrators were Bart Baele and Yves Degryse, founders of the Antwerp-based theatre group BERLIN. In a statement on their website they say it was part of a performance called True Copy, about the life of the prolific Dutch forger Geert Jan Jansen.

They say it “was not a publicity stunt but an essential part of a theatre performance which premiered last Thursday at deSingel in Antwerp.

“The idea is to draw attention to a number of sore points within the art trade. BERLIN invariably links special, personal stories – like the one from Geert Jan Jansen – to universal themes in its shows, with non-fiction often flowing seamlessly into fiction.”

They buried the fake painting on 31 October and sent six anonymous letters, three to Romanian addresses and three a week later to Dutch addresses as a back up plan.

“We then assumed that the Dutch contacts would notify the Romanian or Dutch authorities. Ms Feticu and Mr Westerman, however, took a plane to Romania and the outcome is known. We were surprised at the speed with which the discovery made the press, even before the work’s authenticity had been verified.”

The purpose was to show how the Picasso could make it back to the collection from which it was stolen in 2012. “We never assumed this would be easy, but wanted to find out at which point in the process things would falter, with whom and why. The work is one of the storylines of a performance, which as a whole focuses on the value of truth. What is real and what is not?”

Feticu has said she feels “angry and sad.” Westerman was more sanguine, writing on his Facebook page that he and Feticu had “ended up in a play by Eugene Ionescu” but it could have been worse.

The events in Bucharest are the latest in a long line of art world pranks and hoaxes with no-one better at it than Banksy who recently staged one of his most audacious stunts. He managed to fit a shredder into one of his painting being auctioned at Sotheby’s, activating it moments after the hammer went down.