Bush was captured on video giving an apparent "blank stare" immediately after being told of the attack on the World Trade Center in New York, while visiting a Florida classroom.
He has often been ridiculed for his apparently dazed response.
Now, in a rare interview with the ''National Geographic Channel'', the former US President reflected on what was going through his mind when he was informed that a second passenger jet had hit World Trade Center.
"My first reaction was anger. Who the hell would do that to America? Then I immediately focused on the children, and the contrast between the attack and the innocence of children," ''The Daily Telegraph'' quoted Bush as saying.
Bush said he could see journalists at the back of the classroom getting the news on their own cell phones "and it was like watching a silent movie". He said that he quickly realised a lot of people beyond the room would be watching for his reaction.
"So I made the decision not to jump up immediately and leave the classroom. I didn't want to rattle the kids. I wanted to project a sense of calm," he said of his decision to remain seated and silent.
"I had been in enough crises to know that the first thing a leader has to do is to project calm," he added.
The National Geographic Channel will broadcast the hour-long interview on Aug 28 as part of a week of programs on the cable network called "Remembering 9/11" that mark the 10th anniversary of the attacks.