SWIMMING along the surface, teenager Addison Bethea was on the lookout for scallops when she felt something tugging at her leg.
Expecting to see her half-brother Rhett, she turned around to look - and came face-to-face with a 9ft bull shark.
Addison, now 18, desperately tried to free herself from the terrifying beast as it tore at her right limb.
The high school student was saved by firefighter Rhett, who kicked the shark until it let go - then made a makeshift 4ft tourniquet to save her life.
Addison's story features in a new BBC One documentary - Why Sharks Attack - which airs tonight.
The pair were diving for scallops last July when the shark struck about a mile-and-a-half off the coast of Keaton Beach near Grassy Island in Taylor County, Florida. The water was just 5ft deep.
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Addison, of Perry, Florida, recalled: “I felt something grabbing me. I thought it was Rhett as it pulled me under because I didn’t feel any pain or anything.
“But then it started kind of shaking me and that’s when I knew it was something else.
“It started biting into my right thigh and I was gouging its eye to get it off me and then it started swimming away with me still in its mouth.”
Addison’s half-brother Rhett Willingham describes how he punched and kicked the shark until it let go of her.
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"I heard Addison yell and she surfaced and I immediately could see this tail, just slashing back and forth," he said.
“I grabbed her and started hitting it to get it off.”
Rhett, 23, managed to get Addison to their small boat and they were picked up by a larger vessel which spotted they were in distress and took them to Keaton beach.
The documentary reveals footage of Addison after their boat landed ashore and shows Rhett struggling to keep her conscious.
He tells the first police officer on the scene: “Dude it was huge and I literally had to pry it off her.”
Addison is heard screaming "Help me” as Rhett tells her: “We’re not losing you.”
Addison recalls: “Rhett kept tapping me on my face and saying 'You’re going to be okay' and I said, ‘Okay’.
“You obviously just want to go to sleep because you’re in shock and keep passing out and (I was) losing a lot of blood.”
Addison was airlifted to Tallahassee Memorial Hospital where she had emergency surgery to save her life.
Rhett says: “Once the burden of having to deal with that (saving Addison) was off me, I was like, holy cow, that’s quite deep man.”
Addison, a keen cheerleader and tennis player, later told how she tried desperately to get the shark off her by trying to punch it on the nose, but couldn’t reach due to the way it had clamped its jaws on her thigh.
She said: “I remember from watching Animal Planet you’re supposed to punch them in the nose or something - but I couldn’t get around to his nose the way he bit me.”
Dad Shane hailed his son a hero, saying: “If Rhett hadn’t been there, we would be at the funeral home instead of the hospital. That boy is the definition of a hero.
“The shark attacked Addison’s right leg, front quad muscle. It was completely annihilated. It was devastating, a nasty, nasty wound.
The shark attacked Addison’s right leg, front quad muscle. It was completely annihilated. It was devastating, a nasty, nasty wound
Addison's dad, Shane
“The vascular surgeon took the vein from the left leg and turned it into an artery for the right leg to get blood flow.”
Six days after her first surgery Addison had an operation to amputate her leg above the knee - and took her first steps using a walker the next day.
Statistics show you are more likely to be bitten by a shark in America than anywhere else, with the US confirming 41 bites out of 57 worldwide last year - one of which was fatal.
Florida is the hotspot for attacks, with 16 victims last year. The most dangerous spot is Volusia County, which includes the popular resort Daytona Beach.
Last year sharks bit 16 people in encounters off Florida’s waters.
Among the victims, people swimming and wading were most likely to be bitten, followed by surfers and board sports, then snorkelers and divers.
The odds of being attacked and killed by a shark are one in 3.7million, according to the Florida Museum of Natural History.
The predator that bit Addison is most likely to be a bull shark, which have been known to attack spear fisherman, according to Professor Gavin Naylor, a researcher for the Florida Program for Shark Research.
He said changing environments mean sharks are drawn to different areas in search of food “which might prompt them to bite humans when they otherwise wouldn't”.
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"I'm surprised Addison was bitten because you don't get many shark bites in this area," he added.
Why Sharks Attack airs on BBC One tonight at 8pm.