The chess world is in turmoil after the reigning five-time world champion Magnus Carlsen mysteriously withdrew part way through a tournament for the first time in his career.
Carlsen was three rounds into the nine-round $500,000 Sinquefield Cup when he announced he was pulling out.
"I've withdrawn from the tournament," Carlsen tweeted on Tuesday morning (AEST).
"I've always enjoyed playing [at the Saint Louis Chess Club], and hope to be back in the future."
Attached to the tweet was a video of soccer manager Jose Mourinho saying: "I prefer not to speak. If I speak I am in big trouble … and I don't want to be in big trouble."
The cryptic tweet immediately prompted vigorous debate about the reasons for Carlsen's withdrawal, including speculation that it could be in protest of suspected foul play.
Yesterday Carlsen suffered an upset loss with the white pieces to 19-year-old American Hans Niemann, a self-taught rising star who is drawing comparisons to the great Bobby Fischer.
"I think he was just so demoralised because he's losing to an idiot like me, you know?" Niemann said after the game.
"It must be embarrassing for the world champion to lose to me. I feel bad for him."
Carlsen's surprise loss ended his streak of 53 undefeated classical games, putting a big dent in his goal to become the first player to reach a 2900 rating.
"I think that Magnus believes that Hans probably is cheating," said American grandmaster and popular chess streamer Hikaru Nakamura.
"You really have no way of proving that, if you really believe that, so I think Magnus's way of basically saying that is he's not going to actually say it, but he's putting out the stuff saying 'if I talk I'm in trouble', and he's withdrawing to make the point without publicly making the point."
Other commentators were sceptical that Niemann would — or could — have cheated in his 57-move win over the world champion.
"If this is based on the game alone, then this sounds like a most frivolous accusation," Uzbek grandmaster Rustam Kasimdzhanov told chess24.
"If there was anything else that was amiss, or whatever, then maybe it's up to the organisers to explain it. We cannot be sitting here guessing. We just have no information."
Internet chess personality Levy Rozman believes the repercussions could be enormous.
"[This withdrawal is] most likely the biggest chess scandal in history … the chess world is shaken to its core because nobody knows what's going on now," said the 26-year-old International Master.
"The only way to [cheat], live, over the board, person-to-person, someone has to be getting assistance.
"It's happened. People walk to the bathroom, they have a phone they've hidden, they communicate with signals — but you would think, at a tournament like the Sinquefield Cup — where they probably have metal detectors, they get patted down — there is nothing you can bring on you that somehow brings messages to your body.
The Grand Chess Tour announced just an hour after Carlsen's tweet that it would be implementing additional anti-cheating precautions for the Sinquefield Cup's fourth round.
Niemann said the controversy surrounding Carlsen's withdrawal distracted him from his fourth-round match against fellow teenager Alireza Firouzja, which ended in a draw.
"I'm speechless to be honest. It's very weird" he said.
"I don't want to draw any conclusions. It's very strange, but at least I got to beat him before he left."
