The international community of professional chess was shaken over the past week by accusations of cheating, after a 19-year-old relative newcomer toppled a celebrated world champion in a major high-stakes tournament in the United States.
American player Hans Niemann beat Norwegian grandmaster Magnus Carlsen, 31 - rated the world's top player by the International Chess Federation (FIDE) - in the third round of the prestigious Sinquefield Cup last Monday.
The shock defeat by Mr Niemann, who is ranked world no. 40, ended Mr Carlsen's 53-game unbeaten streak.
The loss was swiftly followed by the Norwegian grandmaster's announcement, without explanation, that he would withdraw from the tournament entirely.
"It must be embarrassing for the world champion to lose to an idiot like me," Mr Niemann said in an interview shortly after his victory. "I feel bad for him."
In a tweet later, he wrote: "This is truly a humbling day for me. I am eternally grateful for the opportunity to play chess at the highest level and live out my dreams. A few years ago, my chess dreams were quickly dwindling but thankfully they rose from the dead."
Mr Carlsen said nothing else publicly beyond his withdrawal from the tournament. But he posted a cryptic tweet featuring a 2020 speech by football manager Jose Mourinho saying: "I prefer not to speak. If I speak, I am in big trouble."
The Portuguese manager had made the comments while protesting the result of a match, suggesting foul play.
A spokesman for Mr Carlsen did not respond to a request for comment.
The chess world was quick to pick up on the implications of Mr Carlsen's latest move, with the media dredging up Mr Niemann's history for having once been kicked off an online gaming site for using a computer to analyse his moves.
"I think Magnus believes that Hans probably is cheating," said Mr Hikaru Nakamura, an American grandmaster ranked No. 6 in the world.
Mr Nakamura added, however, that the allegation remained "unproven".
FIDE director-general Emil Sutovsky noted that Mr Carlsen was not the type of player to quit the tournament over petty spite.
"No matter how his tournaments went, Carlsen never quit. He must have had a compelling reason, or at least he believes he has it," Mr Sutovsky wrote in a tweet. "Don't call him a sore loser or disrespectful."
Even Tesla co-founder Elon Musk weighed in on the debate online, sharing a tweet in which a Twitter user said he was obsessed with the notion that Mr Niemann was cheating using "wireless anal beads that vibrate him the correct moves".
Mr Niemann has denied ever cheating at over-the-board chess, though he admitted to having previously cheated while playing online as a child.
Organisers of the tournament have not found any evidence of foul play so far, and have instituted additional fair play protocols, the Wall Street Journal reported.
But cheating in over-the-board chess has traditionally been hard to prove, with cheaters often obtaining outside-move advice through hidden communications systems.
The event's organisers declined to comment on the motivations behind Mr Carlsen's withdrawal.
"A player's decision to withdraw from a tournament is a personal decision, and we respect Magnus' choice," Mr Tony Rich, executive director of the Saint Louis Chess Club, said in a statement. "We look forward to hosting Magnus at a future event in Saint Louis."
The Sinquefield Cup, which features cash prizes of up to US$350,000 (S$490,000), is a key step towards the World Grand Chess Tour. Mr Carlsen won the cup twice in the last decade, and had never before withdrawn from an ongoing event, Vice News reported.