Chess world champion Magnus Carlsen (31) caused a bang. After his defeat on Sunday against the American Hans Niemann (19) at the Sinquefield Cup in St. Louis (US state of Missouri), the Norwegian withdrew from the tournament prematurely – he had never done so in his entire career.

Carlsen followed his departure with a nebulous tweet that raised suspicions of cheating. Carlsen wrote: “I have retired from the tournament. I’ve always enjoyed playing at the St. Louis Chess Club and hope to return at some point.”

Carlsen garnished his tweet with a video excerpt from an old interview with football coach José Mourinho (then at Chelsea). After a defeat at Premier League rivals Aston Villa, he said in front of the cameras: “I prefer not to speak. If I speak, I’m in big trouble.”

What is Carlsen trying to imply with his tweet? For the chess community, the matter is clear: Carlsen accuses his opponent of cheating, but does not want to say so publicly. Other prominent chess players are less squeamish. Top chess streamer and multiple US champion Hikaru Nakamura pointed out that Niemann had been banned twice in the past for cheating.

The Canadian grandmasters Eric Hansen and Aman Hambleton made the most violent accusation: in a Twitch live stream, they suspected that Niemann might have used manipulated anal beads that were supposed to “show” him the right moves with the appropriate signals. Niemann could have inserted one of the sex toys and received remote control vibrations, possibly from a helper.

The theory quickly went viral and was even picked up on Twitter by Tesla boss Elon Musk. He defaced a wisdom of the philosopher Arthur Schopenhauer. He had formulated: “Talent hits a target that no other hits; genius hits a target no one else sees.” Musk added in parentheses after that, “Because it’s in your buttocks.”

It may be impossible to prove the allegations. Nevertheless, Niemann felt compelled to react. In an interview, he admitted to having cheated while playing – once at the age of 12, once at the age of 16, both in online tournaments. He expressed remorse for his cheating at the time, explaining: “I cheated on random games on I was confronted with it. I stood. And that is the biggest mistake of my life.”

He tried to make up for his missteps by winning live events: “That was my mission. And that’s why I lived out of a suitcase and played 260 games in a year, trained twelve hours a day because I have something to prove.”

Niemann then retaliated and accused Carlsen and other top players of wanting to destroy his career. His offer: “If you want me to strip completely naked, I will do it. Because I know I’m clean.”

An answer from the world number one Magnus Carlsen is still pending.