CANNES, France — Becket is the illegitimate son of a wealthy New York dynasty: His mother, an heiress from a family of financiers, eloped with a jazz musician. Becket feels entitled to a share of the family riches, but his evil grandfather is standing in the way.

That’s the premise of “Rothchild,” an upcoming black comedy starring Shia LaBeouf (as Becket) and Mel Gibson (as the grandfather) that was announced at the start of the Cannes Film Festival. The festival, a 12-day event that ends May 25, is an indisputable hub of glamour and spectacle, but it is also an occasion for haggling and deal making — a marketplace where merchants sometimes flaunt movies that haven’t been made yet, in the hope of drawing media attention and attracting film buyers.

The media attention part clearly worked for “Rothchild.” Parallels were drawn with the Rothschilds, perhaps Europe’s most storied banking family. The announcement was covered by an array of global outlets, followed by social media outrage that Gibson, who made anti-Semitic remarks after he was arrested on suspicion of driving under the influence of alcohol in 2006, should headline the movie. The Rothschilds, of course, are Jewish, and Gibson’s character was described as a sinister grandfather, making some wonder if it was too perfect a role for him.