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.