On Sept. 11, 2001, then-president George W. Bush was reading The Pet Goat to a classroom of second graders at Emma T. Booker Elementary School in Sarasota, Florida, when a whispered word in his ear rocked his young presidency - and the images of burning towers on TV screens across the nation changed the country and the world.

PHOTOS: Moment Bush Learned of 9/11 Terror Attacks

Bush's then-press secretary, Ari Fleischer, was with the president on that fateful day, from the moment Bush learned about the attacks to his fly around the country on Air Force One to his return to Washington to address the nation that night. Today Fleischer is reliving the minute-by-minute details of 9/11 live on Twitter, and adding some of his own reflections 13 years later. Here's a look:

8:40am, 9-11, 2001: I was in the motorcade 4 the drive from the Colony Beach & Tennis Resort in Sarasota, FL 2the Emma Booker Elem. School.

- Ari Fleischer (@AriFleischer) September 11, 2014

Approx 8:50: I got a page on my pager (we didn't have blackberries then and the iPhone hadn't been invented) telling me a plane hit the WTC.

- Ari Fleischer (@AriFleischer) September 11, 2014

After the President finished shaking hands, Karl Rove informed him of what we thought had to be an "accident."

- Ari Fleischer (@AriFleischer) September 11, 2014

I suspect by now most people are watching TV, watching events unfold. I was in the classroom with the President watching the reading event.

- Ari Fleischer (@AriFleischer) September 11, 2014

9:03 United Flight 175 crashes into the South Tower.

- Ari Fleischer (@AriFleischer) September 11, 2014

9:05 WH Chief of Staff Andy Card interrupts the Pres to whisper in his hear - the second tower has been hit. "America is under attack."

- Ari Fleischer (@AriFleischer) September 11, 2014

Bush said later he stayed 2collect his thoughts and send a signal of calm. He said he didn't want 2bolt from his chair and alarm the nation.

- Ari Fleischer (@AriFleischer) September 11, 2014

POTUS left the event and went into the holding room 2get briefed/ work the phones. Here is a picture of the scene. pic.twitter.com/ZztLy2plSl

- Ari Fleischer (@AriFleischer) September 11, 2014

Someone wheeled a TV into the holding room. Here's the scene: pic.twitter.com/x9A3RTQykd

- Ari Fleischer (@AriFleischer) September 11, 2014

Here's what Bush said: Today, we've had a national tragedy.

- Ari Fleischer (@AriFleischer) September 11, 2014

Terrorism against our nation will not stand. And now, if you'd join me in a moment of silence.

- Ari Fleischer (@AriFleischer) September 11, 2014

9:37 American Airlines Flight 77 crashes into the Pentagon.

- Ari Fleischer (@AriFleischer) September 11, 2014

POTUS is told of attack on the Pentagon by either the Secret Service in the front of the limo, or by Condi on the phone. I don't remember.

- Ari Fleischer (@AriFleischer) September 11, 2014

FOne Capt. Mark Tillman told me 10 yrs later that we took off at unusually steep ascent bcause he had a report of a sniper at end of runway.

— Ari Fleischer (@AriFleischer) September 11, 2014

9:59 The South Tower of the World Trade Center collapses.

— Ari Fleischer (@AriFleischer) September 11, 2014

10:07 United Flight 93 crashes in a field in Pennsylvania.

— Ari Fleischer (@AriFleischer) September 11, 2014

After the 3rd plane hit the Pentagon, we were told there were 3 aircraft "missing". After Flight 93, we thought 2 more attacks coming.

— Ari Fleischer (@AriFleischer) September 11, 2014

"A call came into the switchboard saying 'Angel is next,'" Bush said. 'Angel' was the codeword for Air Force One.

— Ari Fleischer (@AriFleischer) September 11, 2014

Bush also told VP - and I quote - "We're at war Dick and we're going to find out who did this and we're going to kick their ass."

— Ari Fleischer (@AriFleischer) September 11, 2014

Here is a copy of one page from my notes while all this was going on: pic.twitter.com/xpqWXWLMAQ

— Ari Fleischer (@AriFleischer) September 11, 2014

Here is a scene aboard AFOne in POTUS's cabin, enroute Barksdale. pic.twitter.com/ayAgN7Efuv

— Ari Fleischer (@AriFleischer) September 11, 2014

Sonya Ross of AP., Ann Compton of ABC, Doug Mills a NYT photographer, a cameraman and soundman stayed on board.

— Ari Fleischer (@AriFleischer) September 11, 2014

Jay Carney, then with Time Magazine, was left behind at Barksdale. He was VERY displeased.

— Ari Fleischer (@AriFleischer) September 11, 2014

4:30 Pres. Bush called Mrs. Bush. "I'm coming home…see you at the White House."

— Ari Fleischer (@AriFleischer) September 11, 2014

This is a developing story. Continue to check back for updates throughout the day.