Sunday marks the 21st anniversary of the attacks on the World Trade Center.

George Pataki was the governor of New York on Sept. 11, and he said he knew the state was under attack as soon as the second plane hit the Twin Towers.

"When the second plane hit, we were being attacked," Pataki told Rocco Vertuccio and Shannan Ferry Saturday morning on NY1. "You just had to immediately spring into action."

Pataki activated the state's emergency response plan, which included deploying the National Guard, state troopers and mutual aid for fire support.

But the hardest thing Pataki says he had to do after the attacks was meet with the families of the victims.

"That was pretty much the hardest part — meeting with those family members," Pataki said. "Because we all lost friends, people we knew. We had this horrible sense of loss, but compared to losing your son or daughter, mother or father. It was just a horrible thing."

The attacks changed how Pataki led New York, making him realize that he could no longer take anything for granted.

"You saw friends and you were sure that you'd see them tomorrow, and then, all of a sudden, because of these hideous, hideous attacks, they were gone," Pataki said. "So you realize that you had to appreciate the freedoms we had, the people, the friends, the families we had every single day and not take tomorrow for granted."

Almost 21 years later, Pataki is proud of the courage New Yorkers showed when recovering from the attacks.

"If there was anything positive, [it] was how united we were. We were all New Yorkers. We were all Americans. We weren't Republicans, Democrats, Black, white," Pataki said. "We had been attacked. We were going to stand together. We were going to rise together and we were going to reach new heights together, and we did, and I think looking back 21 years later, we can all be proud of it."

However, looking forward, Pataki is concerned that the city's youth will forget about the tragic events that took place on Sept. 11, 2001.

The 9/11 Tribute Museum in lower Manhattan closed in August after being unable to recover from losses caused by the COVID-19 pandemic.

"I fear 21 years later, too many people aren't aware of the consequences of not being vigilant and protecting ourselves from those who will attack us again," Pataki said. "We have to continue to teach the story of those heroes — of the wonderful people we lost — and what we have to do to make sure that doesn't happen again."