Daniel Whiffen made history by winning the 800m freestyle final in Doha, becoming Ireland's first world swimming champion.
The 22-year-old won the gold medal with a time of 7:40.94.
Wiffen had a sensational swim, timing his swim perfectly and taking the lead with 50 meters to go.
He surged ahead of Australia's Elijah Winnington and Italy's Gregorio Paltolinieri to win his first world title.
“Obviously the goal going into this event was for Ireland to win a world medal and get on the highest podium and this is obviously Ireland's first medal at World Championship level.” said Wiffen.
“Well, I'm really happy to hear that, and I'm really happy.”
Wiffen, from Magherarin, qualified for the final in second place, but was led from the outside lane in the early stages.
Eight-lane Winnington set a world record pace in the intermediate stages, leading Paltrinieri in one lane, with Wiffen in the middle of the pool in third place, 1.54 seconds behind.
The Australian, who had won silver in the 400m freestyle earlier in the championships, began to tire and the Italian took the lead with 200m remaining.
Wiffen raced at a great pace and began to involve Paltolinieri. As they took their final turn together, Wiffen moved forward.
He turned on his power with 50 meters to go and was the first to touch the wall, beating Paltrinieri over two seconds ahead of Winnington to take the silver medal.
“I was just trying to build confidence in myself and see if I could trust it and actually execute my race plan and that's what I did. So I'm very happy.” Wiffen added.
“I hope I don't get too emotional on the podium, but yeah, I'm just ecstatic and can't wait to get on this podium and grab a medal.”
It was a particularly satisfying result for Wiffen, who finished fourth in the 800 meters and 1,500 meters at last year's world championships in Japan.
Wiffen also broke the 800m short course world record in Bucharest in December, and Wednesday's victory in Doha marks another key checkpoint in his quest to become Olympic champion in Paris this summer. Ta.
Wiffen hopes to add the 1500m title to his 800m gold medal with long-distance heats starting Saturday morning.