A Team GB swimmer saw his Olympic dream cut devastatingly short after he was disqualified for swimming too long underwater despite finishing first in his race.
Luke Greenbank thought he had advanced from his 200m backstroke heat when he comfortably touched the wall first.
The double Olympic medallist clocked a time of one minute 56 seconds more than a second ahead of Hungarian favourite Hubert Kos but his joy turned to despair after it emerged he fell foul of the infrequently seen World Aquatics rule.
The regulation, which has been in place since 1988, states competitors cannot swim more than 15 metres underwater at the start of each turn. By that point, their head must be above the surface.
Greenbank, whose time would have seen him qualify fastest for the semi-final on Wednesday evening, remained completely submerged over a 15 metre stretch after the third turn, meaning he breached the rule.
The 26-year-old Crewe swimmer was visibly shocked as he looked up at the screen immediately after his race to learn his fate and looked in complete disbelief as he held his head in his hands. Its really annoying, I feel like Im on good form, he said afterwards, adding that he was absolutely gutted.
Greenbank, who was one of the favourites to add to Great Britains medal tally in the pool, had no grounds to contest the decision after replays showed he clearly remained underwater when he passed the red marker.
The full rule, which applies to the backstroke, butterfly and freestyle events but not breaststroke, stipulates: Some part of the swimmer must break the surface of the water throughout the race. It is permissible for the swimmer to be completely submerged during the turn, at the finish and for a distance of not more than 15 metres after the start and each turn. By that point the head must have broken the surface.
Greenbank won a silver and a bronze in the 4x100m medley and 200m backstroke respectively at the Tokyo Olympics. He was also crowned world champion in the same medley event in 2019 and followed it up with another gold at the Commonwealth Games in Birmingham.
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