Out of all the stories that have come out of the tragic day 21 years ago today, this 9/11 story is quite incredible.
It concerns to two very brave men - Brian Clark and Stanley Praimnath - who escaped Twin Towers with just four minutes to spare.
Mr Clark is a Canadian businessman whose office was struck by one of the planes. Mr Praimnath is the man whose life he saved on the way down from the World Trade Centre.
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Brian Clark recalled the extraordinary turn of events in an interview with the Associated Press ten years ago.
On 11 September 2001, Brian Clark was on the 84th floor of the World Trade Centre's South Tower.
Just minutes after he started work, at 9.03am, Flight 175 struck floors 77 to 85 of the building.
Clark said: "Our room just got rocked, just destroyed in a second.
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"And it was for the next 10 seconds after that immediate impact – that was the only 10 seconds of the day that I was afraid. Terrified, in fact.”
Mr Clark then said he had a decision to make - what staircase would he take to try and get out of the crumbling building safely.
He chose staircase A, which luckily for him was the only staircase that hadn't been destroyed.
As Mr Clark and his co-workers headed down the stairs, they were told to turn back as there was fire and debris on lower floors.
The woman's advice was to head to the roof and wait for a helicopter she said would rescue them.
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She then headed up to the roof while Mr Clark and his colleagues deliberated on what they should do.
At this point, the Canadian Businessman heard a banging noise on the 81st floor.
"'Help! Help! I’m buried! Is anybody there? I can’t breathe,'" a voice said.
Mr Clark left the group and headed towards the voice in an attempt to save them.
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He said that amongst the debris, he saw a hand sticking out through a hole in a wall, waving up and down.
"Hallelujah, I've been saved," the man screamed.
This was Stanley Praimnath who ducked under his desk as Flight 175 approached the tower.
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Mr Praimnath's actions were very important as the desk shielded him when the office collapsed.
After several failed attempts, Mr Clark eventually got Mr Praimnath out of the ruble and headed back towards the staircase.
At this point, Mr Clark's colleagues who he initially came down with were no longer there as they headed upstairs to be rescued.
The rescue never came, and none of them would survive.
Mr Clark and Mr Praimnath began walking down the 80 flights of stairs and eventually encountered the debris they were warned about, but were able to move it aside.
At 9.55am, the pair reached the ground floor and were told to run by firefighters.
Just four minutes later, the South Tower began collapsing - only four people in the floors above where Flight 175 crashed survived - Mr Clark and Mr Praimnath were two of them.
The two of them are now 'brothers for life'.
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Topics: US News