https://www.vice.com/en_us/article/epz5n7/magnus-carlsen-hans-niemann-has-cheated-moreand-more-recentlythan-he-has-publicly-admitted

World chess champion Magnus Carlsen released a scathing statement addressed to the “chess world” Monday afternoon that said he is “not willing to play chess with [Hans] Niemann,” and that “I believe that Niemann has cheated more—and more recently—than he has publicly admitted.” That statement is by far Carlsen’s most extensive in the ongoing cheating saga that has captivated chess and spilled out into the broader consciousness. 

Earlier this month, Niemann defeated Carlsen at the Sinquefield Cup chess tournament; it was a huge upset because Niemann was ranked far lower than Carlsen and because he was playing as the black pieces (which goes second and has an inherent disadvantage). Carlsen pulled out of the tournament altogether, and implied at the time that he believed Niemann was cheating. A week later, the two played again at another tournament. Carlsen made one move, then resigned.