Norwegian world champion Magnus Carlsen has publicly accused American 19-year-old grandmaster Hans Niemann of cheating. It comes after Carlsen’s defeat to Niemann at the Sinquefield Cup on September 4th and when Carlsen resigned on move 1 as a protest in another game vs Niemann in the Julius Baer Generation Cup.

In a statement on Twitter released this Monday, Carlsen “believes that Niemann has cheated more than he has publicly admitted.” He added, “his over the board progress has been unusual, and in our game in the Sinquefield Cup I had the impression that he wasn’t tense or even fully concentrating on the game in critical positions, while outplaying me a way I think only a handful of players can do.”

Hans Niemann is an American Grandmaster who has risen to fame, after gaining 300 points in only 3 years. He has admitted to cheating earlier in his chess career online twice at the age of 12 and 16, but said he had never cheated in an over-the-board game.

Despite this, Magnus Carlsen did go on to win the Julius Baer Generation Cup.

Cheating in chess is treated very seriously. In 2015, Georgian grandmaster Gaoiz Nigalidze was caught cheating for using electronic devices in a bathroom. He was banned for 3 years and had his Grandmaster title revoked.

An investigation by FIDE is currently ongoing.