Jessica-Jane Applegate swam a perfectly controlled race to claim ParalympicsGB's third gold medal in the pool with victory in the S14 200 metres freestyle.
Applegate, who turned 16 less than a fortnight ago, had qualified fastest after breaking her own British record this morning.
Tonight she was fourth at the halfway stage before making a move on the third length and was in the bronze medal position with 50m to go.
The City of Norwich swimmer then produced a storming final length to overhaul her rivals and was pulling further ahead when she touched in two minutes 12.63 seconds.
Applegate had an operation on her foot a month ago putting her participation in doubt.
Not only did she compete but her time was a Paralympic record.
"I'm just so happy," she told Channel 4. "It means so much. I just want to thank my mum and my family and everyone who's supported me. I'm on cloud nine at the moment."
Asked how she came back to win, she said: "I really have no idea."
Victory sees Applegate join Ellie Simmonds and Jonathan Fox as Britain's gold medallists at the Aquatics Centre, her medal the 13th claimed so far by the home swimmers.
Applegate, who had already come fourth in the 100m backstroke, added: "I am ecstatic, I really didn't think I could do something like that.
"At the last turn I could see how far ahead they were and I knew I had to give everything I had. It was my last race so I knew it didn't matter if I collapsed at the bottom of the pool, it's fine."
In the men's equivalent, Daniel Pepper and Ben Procter finished seventh and eighth respectively.
Pepper and Procter had qualified fourth and fifth prompting hopes of gatecrashing the podium.
However, the pace was blistering and resulted in Jon Margeir Sverrisson setting a new world record of 1:59.62, with the first three men all dipping under two minutes.
Procter, third in the 2010 World Championships, started the better of the two Britons and was third at halfway with Pepper in seventh.
However, Procter could not maintain his pace and found the field overtaking him as he finished in 2:03.30 with Pepper 0.03secs ahead.
James Clegg picked up Britain's second medal of the night in the S12 100m butterfly when he took bronze.
The 18-year-old touched out in a close finish to claim third in 1:00.00 after turning at the halfway point in fifth.
It meant a quick dash for his family over to the athletics with his sister Libby set to compete in the 100m final at 1955.