Adam Peaty sensationally won Britain's first medal of the 2016 Rio Olympics by taking gold in the men's 100 metres breaststroke and setting a new world record.
The 21-year-old stormed to victory in 57.13 seconds, smashing his own world record for the second time in two days to scoop Britain's first men's swimming gold in decades.
As the historic victory sank in he proclaimed: "I did it for my country because that means so much to me."
Fellow athletes and members of the Team GB camp, including sprinter Asha Philip, were ecstatic about the news.
Peaty dominated his first Olympic final, beating second-place South African swimmer Cameron van der Burgh by a body length and slicing nearly half a second off the world record mark he set in qualifying.
The spellbinding swim was followed just minutes later with glory for Team GB's Jazz Carlin, who took silver in the women's 400 metres freestyle.
Describing the historic moment as "crazy" and "so surreal", the seemingly unflappable Peaty said he took the first 50 metres "easy" before bursting back along the home straight "with everything I've got".
Giving a thumbs up as he received his medal, the patriotic champion smiled ear-to-ear and - in contrast to many victorious Olympians - sang the national anthem before waving to his family in the crowds.
He said afterwards: "I want to thank the whole of Britain, my country, the Royal Family and everything that makes me proud to be British."
It was the culmination of seven years of training for the City of Derby swimmer, who said a pep talk from head of British Swimming, Bill Furniss, to "burn the boats, move forward and attack" helped him to shrug off the huge anticipation surrounding his bid.
He said: "I wasn't scared of anyone, it was complete tunnel vision.
"I am just so happy for British Swimming now, for Team GB because it's the first gold of the games and what better than to come from swimming."
It is the first men's Olympic gold by a British swimmer in 28 years, since Adrian Moorhouse's success in the same event in Seoul 1988.
A surprise star of Peaty's story has been his adoring grandmother, Mavis Williams, who roared him on in the early hours of Monday morning from her home in Sheffield.
Needless to say, the internet shared Olympic Nan's joy.
Cheering him on from the poolside were his mother and father, Caroline and Mark Peaty, and girlfriend Anna Zair.
His mother said she was "ecstatic", while his father appeared lost for words.
"It was good. Very good. He's got two world records in the matter of two days," he said.
Moments after his victory Carlin buried her Olympic pain in spectacular fashion by winning a silver medal in the women's 400 metres freestyle.
The 25-year-old from Swansea was heartbroken after missing out on selection for London four years ago.
But only Katie Ledecky of the US was able to better her in Rio as Carlin posted a second personal best of the day.
She said: "Four years ago I was in the stand cheering everyone on and now I've actually been a part of the team and to come away with a silver medal, I'm absolutely over the moon.
"I'm so grateful to everyone at home that's been supporting us and to get up and watch us at ridiculous hours of the morning."