A chess grandmaster from Minnetonka was forced to forfeit his latest championship game – and blamed it on unexpected visit from his estranged mother.

The U.S. Chess Championships confirmed on its website that 21-year-old Wesley So had to forfeit his match against fellow grandmaster Varuzhan Akobian Friday for writing personal notes on a separate sheet of paper.

This goes against championship rules and as he had been warned twice about it earlier in the championships, a forfeit was declared.

But So's forfeit became steeped in intrigue after the Star Tribune reported that the world number 8's performance may have been affected by a visit from his estranged mother on the eve of the tournament.

The Lake Minnetonka Magazine explains that So was fostered by Lotis Key and Renato Kabigting in 2014 after deciding to drop out of Webster University in St. Louis and pursue a career in chess full-time, after he won the $100,000 Millionaire's Open last year.

The Star Tribune said his biological mother was not happy with this decision, and got in contact with her son within minutes of his arrival at a hotel in St. Louis before the championships started, leading to several "strident encounters" which his foster family says has thrown him off his game (he has now lost 4 out of 9 games this week.)

"There are personal problems in my family," So told the newspaper after the forfeit. "Trying to fix them during this tournament caused a lot of stress and tension. It diverted a lot of energy from the board when I should be focusing on my game."

So's opponent Akobian told Rappler that he had been put off by So's note-writing, saying: "He was probably writing things to encourage himself, but it disturbed me."

"I have been having trouble concentrating so I wrote a note to myself on a piece of paper (not my score sheet) ...it said: double check triple check use your time," So said on his Facebook page. "Akobian saw it and complained to the arbiter and a forfeit was declared. I'm sorry I did not know it was against the rules."