On Thursday, an unused 1936 cover for Belgian illustrator Hergé’s Tintin comic book “The Blue Lotus” was sold at auction in Paris to a private collector for $3.9 million ($1 million above its estimate), becoming the most expensive piece of comic-book art in history. This in itself is not a surprise, given that the previous most expensive comic-book art in history—a two-page illustration, which sold for $3.2 million in 2014—was also drawn by Hergé. However, the “Blue Lotus” sale has been subject to enough controversy to dizzy even the most dedicated Tintinologist.

The work, by all accounts, is absolutely beautiful. A vivid painting in ink, watercolor, and gouache, it depicts Tintin and his wire fox terrier Snowy hiding inside a vase next to an elaborate dragon painting. If that sounds familiar, it’s because a pared-down version of the image forms the cover of “The Blue Lotus.” The one sold this week was rejected by Hergé’s publisher for being, if anything, too beautiful. A work like that would be unfeasibly expensive to reproduce. And this is where the controversy arises.

Belgian artist Georges Remi signed his drawings with the name Hergé—his initials in reverse: R.G.

The official story behind the sale is that the painting was a gift from Hergé, real name Georges Remi, to the seven-year-old son of his publisher, Louis Casterman. However, a man named Nick Rodwell has chosen to contest this. And Rodwell is arguably the biggest Tintin fan of them all. Not only did he open London’s first-ever Tintin shop, but he then married Hergé’s widow, almost 20 years his senior; became head of the Hergé Foundation; and maintained such an ironclad grip on the rights to Tintin that one professor of comics went on record describing him as “one of the most disliked people in European comics.”

The previous most expensive comic-book art in history—a two-page illustration, which sold for $3.2 million in 2014—was also drawn by Hergé.

Experts believe that Hergé never, or at least rarely, gave gifts to anyone without writing a dedication. They claim that a more likely explanation is that Hergé painted the picture, folded it into three, placed it in an envelope, and sent it to his publisher for approval.

Nick Rodwell, pictured here with his wife, Fanny—Hergé’s widow—once described Tintin as the “Rolls-Royce” of comics.

Once it was rejected, the publisher failed to send it back to Hergé, and, after several years of languishing in a drawer, it was eventually given to Casterman’s son. Rodwell told Le Monde that the painting should not be sold. “I’m not saying it was stolen by Casterman. It was just not returned by Casterman,” he said.

The scrap just shows how beloved Tintin, and especially “The Blue Lotus” cover art, has become. Despite Hergé’s iffy political leanings—he was investigated as a Nazi collaborator after the Second World War—Tintin has grown into a Belgian national treasure and a cherished global brand.

One professor of comics went on record describing him as “one of the most disliked people in European comics.”

“The Blue Lotus” is widely considered to be Hergé’s first masterpiece, the moment he stopped indulging in the lazy stereotypes of Tintin in the Congo and started defining his work by the meticulous research that went into it. To find this, a prototypical cover of the book deemed too beautiful to mass-produce, is like stumbling across the Holy Grail.

Unfortunately for Rodwell, his claim is difficult to substantiate. Under Belgian law, unless theft can be proved, possession is ownership. And so, barring something impossibly dramatic happening, the Casterman estate will profit from this rare find.

If only there were a plucky young reporter willing to risk his life in pursuit of the story.

Stuart Heritage is a Kent, U.K.–based Writer at Large for AIR MAIL