A 12ft painting of the Last Supper which for a decade has hung behind the altar of a country church will this weekend go on display at a gallery with the addition of a disturbing and depressing mystery: who shot Jesus?

The painting is the work of the celebrated portrait artist Lorna May Wadsworth and has travelled to Sheffield for a retrospective of her work at the Graves Gallery.

When the painting was unpacked, Wadsworth spotted something nobody else had. A hole in the right side of Jesus which has subsequently been confirmed as a bullet hole.

“It really upsets me to think that someone was so aggrieved by my portrayal of Christ that they wanted to attack it,” said Wadsworth, a painter known for portraits, including one of Margaret Thatcher, which hangs at the Conservative party headquarters, and one of David Blunkett, which hangs in Portcullis House.

The hole had not been spotted by anyone connected to the church in Nailsworth, Gloucestershire, or anyone transporting it to the show. Wadsworth saw it straight away but thought it was general damage. Through a friend she consulted a ballistic expert who identified it as an air-rifle pellet hole. “It must have been an iconoclastic act. I was in shock all weekend, on the verge of tears the whole time,” she said.

The Jesus in Wadsworth’s painting is the fashion model Tafari Hinds. Using him was a way of challenging perceptions, of asking people to “look with fresh eyes at something you think you know”.

Wadsworth said she had no interest in copying Leonardo and it is purposefully titled A Last Supper. All the disciples are deliberately “hot” young actors and models who she corralled into her east London studio, with the promise of food and booze, on a freezing cold November night in 2008. Judas is a blond-haired, blue-eyed boy she came across in a cafe.

Whoever shot the painting, which is on aluminium, would seem to have chosen their spot purposefully. It is on Christ’s right side, the place a Roman soldier made the final wound into the body of Jesus to be sure he was dead. The chances of ever conclusively getting to the bottom of the mystery of who pulled the trigger – and why – are slim.

The work will go on display at a show celebrating the work of Sheffield-born Wadsworth. Also in the exhibition are portraits of the actors Rupert Friend, David Tennant and Michael Sheen, the writer Neil Gaiman, the milliner Victoria Grant and the 6ft Thatcher in what was the last formal portrait she ever sat for, created over five sittings.

That painting has been described by the art dealer and broadcaster Philip Mould as “arguably the boldest formal life portrait of a prime minister ever painted in Britain”.

Wadsworth’s charcoal cartoon, or preparatory drawing, for A Last Supper has also gone on display in the chapel of the Holy Spirit at Sheffield cathedral where it is due to hang for a year.

The plan for the the main painting is to repair the damage after the Sheffield show before it goes back to Nailsworth, a place it must return to, said Wadsworth. “The joy of this painting was that I painted it not as an academic exercise but as a devotional object that lives in a church.”

• Gaze, a retrospective of paintings by Lorna May Wadsworth, is at the Graves gallery, Sheffield, 9 November to 15 February 2020.