The Worst Move He's Ever Made

FACED an opponent with almost exactly the same rating as mine this afternoon in round three of the open section of the Steve Boniface Memorial at Bristol Grammar School.

I guarantee you will never guess how he blundered:

White to make his 40th move in John McGregor (1882/no ECF) - Spanton (1884/171)

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White played 40.Bg3 - so far, not so bad. Then he went to the loo. I played 40...Nc6, and JM returned just as his time ran out. Heading for the toilets was "the worst move he's ever made." Despite this being a round-three game, JM did not realise the time control was 90 minutes plus a 30-second increment for all moves (no extra time at move 40).
I have now gained 11.4 Fide elo in the tournament.