9/11 is remembered as one of the most devastating tragedies in modern American history.
However, it turns out that many people aren't aware of all the devastating events from the fateful day.
While everyone knows that the Twin Towers tragically collapsed after being hit by hijacked planes on September 11, 2001, seemingly far fewer people are aware that a third tower was also pulled down as a result of the wreckage.
As well as the North and South towers, a much smaller building in the World Trade Center complex - known as Tower Seven - was also knocked down by the fallout.
Many have flocked to a new Reddit thread to share their surprise over the fact that they only recently found out about the ill-fated third tower - and speculate as to whether it had been kept quiet for a reason.
The thread began with a user questioning: "In school, how many towers did you get told fell on 9/11?"
"Because I was told 2. I’m 21 years old. I found out there was a 3rd one less than a year ago, and only because I was browsing a CONSPIRACY website," they continued.
The post added: "That’s messed up, I’m curious if others were also only taught about 2 towers in school or if I somehow totally forgot I was taught about a 3rd tower (unlikely)…"
Despite an investigation into why Tower Seven fell released by The National Institute of Standards and Technology in 2008, many conspiracy theorists continued to suggest that the building was brought down by intentional demolitions rather than by falling debris.
"I remember seeing an explosion at the base of the building on TV," one conspiracy theorist alleged on Reddit.
Another referred to the now infamous BBC news clip in which the fall of Tower Seven is announced before the tower comes down.
"It was also reported live on BBC that tower 7 had fallen, and it was still erect in the background of the reporter," they wrote, adding: "Strange stuff surrounding that Tower."
However, others put conspiracy theories to bed. One user sought to explain how news stations 'predicted' the fall of Tower Seven, saying: "hey reported for hours that tower 7 WILL collapse (because of all the burning debris that very visibly crashed on it), until up from somewhen it was accepted as a given fact."
They added that firefighters at the time "said that it would be highly unlikely if it withheld these damages."