George Bush explained his controversial reaction to finding out about 9/11 attacks

Footage of former President George Bush finding out about the 9/11 terror attacks will always go down as one of the eeriest moments in modern history.

The president had been visiting the Emma E. Booker Elementary School in Sarasota, Florida, and reading a book with a classroom full of children, when he heard the terrifying news.

Andrew Card, who was the White House Chief of Staff serving under Bush at the time, had to deliver the news that a second plane had hit the World Trade Center.

He approached him in the middle of the visit, while a child was reading, and whispered in his ear.

Speaking about it afterwards, Bush said: "Andy Card comes up behind me and says, 'Second plane has hit the second tower. America's under attack'... and I'm watching a child read.

"Then I see the press in the back of the room beginning to get the same message I just got. I could see the horror etched on the face of the news people who had just gotten the same news."

The moment Bush discovered America was under attack (PAUL J. RICHARDS-/AFP via Getty Images)

Meanwhile, Card said of the moment: "I had to deliver a message that the President didn't expect to hear, and that was almost unbelievable.

"But it also, literally, was the message that he had to hear. Whether he wanted to or not."

The footage has since been included in many documentaries of the disaster and will always remain a particularly poignant moment.

Bush heard the devastating news while at a school in Florida (George W. Bush Presidential Library/Getty Images)

Bush's reaction proved to be quite controversial at the time, with some criticising the president over his response.

However, explaining those initial moments in the BBC doc, 9/11: Inside the President's War Room, Bush said: "During a crisis, it's really important to set a tone and not to panic.

"I waited for the appropriate moment to leave the classroom, I didn't want to do anything dramatic, I didn't want to lurch out of the chair and scare the classroom full of children.

"So I waited."

Bush spoke about his response to the terror attack (Spencer Platt/Getty Images)

In hindsight, people have reflected on Bush's response to the disaster, with many changing their views over his reaction.

One wrote: "Wasn't a fan of his, but he did absolutely the right thing here and I think the repeated criticism is unfair. You can tell that he is a father, and he reacted correctly in the environment he happened to be in. He handled this expertly."

While another said: "I was a senior in high school on 9/11. I remember the criticism of President Bush for his reaction… Looking back on it over 20 years later, I’m still confident that he had the reaction a strong leader should have, but damn what a crazy situation to be in when you get that news. Of all places, a classroom reading with children."

And a third added: "He received so much backlash for his reaction from the press. I remember being a kid and seeing how well he handled himself."