The former White House chief of staff, who was pictured whispering in former President George W. Bush’s ear that the nation was under attack on Sept. 11, 2001, called on Americans to remember their promise to never forget the events of that day on its 25th anniversary.

Andy Card, 79, was the White House chief of staff for Bush who had to deliver the news that multiple planes had hit the World Trade Center while the president sat in front of a classroom of elementary school students in Sarasota, Florida.

Card shared his remembrances of that day with Savannah Guthrie on TODAY to mark 25 years since the terrorist attacks that changed the country forever.

“I’m conscious that we have to keep the promise that we made when we said we would never forget,” Card said. “And too many people have moved on and don’t remember to remember.

“But we all promised, so this is a great wakeup call and a conscience-raising response that’s so critical,” he added. “And America is a great country, and the tragedy of 9/11 also was a magnet for all of us to come together as Americans, and we did, and it was so refreshing to see that.”

Bush had been speaking to students on the morning of Sept. 11, and when they paused to take their books out, Card saw an opening to deliver the news to the president.

“A second plane hit the second tower. America is under attack,” Card recalled telling Bush.

He shared that chilling statement and then stepped back “because I did not want to have a conversation with him” due to the presence of microphones from media attending the event. He also didn’t want to upset the students.

Since that day, Card has been working to educate a generation of Americans who have no memory of the 9/11 attacks.

Card, who served as chief of staff from 2001 to 2006, now serves on the Organizing Committee of the 9/11 Legacy Foundation to preserve history, support education and turn “never forget” into active remembrance.

“It’s good to remember, there’s sad things to remember, and there’s obligation because of it,” Card said.

Card also hopes that the unifying spirit that galvanized the country after the 9/11 attacks can be resurrected in a country fractured by politics and culture wars.

“We do not celebrate 9/11,” Card said. “We acknowledge 9/11, we rally because of 9/11. America came together, and America can come together again. And we want everyone around the world to know how strong America is.”