In just over a month, the most expensive artwork ever sold will be unveiled to the public at the Louvre Abu Dhabi. The $450 million portrait, entitled “Salvator Mundi,” depicts a beneficent Jesus Christ with one hand raised in blessing, the other clasping an orb glittering as if suffused with heavenly light. Curls fall over Christ’s shoulders in perfect spirals, easily melting into the painting’s monochrome background, while the folds of his blue smock evince an almost sculptural precision. Still, the craftsmanship evident in the work is not enough to account for its hefty price tag—this honor derives solely from the portrait’s recent identification as one of 16 extant paintings by Leonardo da Vinci.

For all its hype, “Salvator Mundi” has plenty of critics: Vulture’s Jerry Saltz described the work as a “two-dimensional ersatz dashboard Jesus.” The Guardian’s Adrian Searle didn’t mince words either, writing that the painting’s Christ “has the glazed look of someone stoned.” Now, just a month before the work makes its public debut, another historian has joined the debate, asserting that “Salvator Mundi” was painted not by da Vinci, but his studio assistant, Bernardino Luini.

Art historian Matthew Landrus, a research fellow at Oxford University who has authored multiple books on da Vinci, will present his case in an updated edition of a 2006 text, Leonardo da Vinci: 500 Years On: A Portrait of the Artist, Scientist and Innovator, set for release this September.

Landrus tells the Guardian’s Dalya Alberge that he believes da Vinci only contributed around five to 20 percent of the final painting, and that a “comparison of Luini’s paintings with the ‘Salvator Mundi’ will be sufficient evidence” to bear out his argument.

In an interview with CNN’s Oscar Holland and Jacopo Prisco, Landrus says the Renaissance master likely sketched out the initial design and added finishing touches, leaving the bulk of the work to his studio assistants. ...