Ahead of his final year as the principal of Columbine High School, Frank DeAngelis remarks on how he moved forward after the deadly mass shooting. KUSA's Kim Christiansen reports.

The principal of Columbine High School, who led his school during its darkest day 14 years ago, announced this week that he is retiring in 2014. And he said on Wednesday that a pastor's advice got him through the survivor's guilt he felt for living through the April 20, 1999, attack.

"All the people that survived that day, we're all suffering from survivors' guilt," principal Frank DeAngelis told NBC affiliate KUSA in Denver, a day after he announced plans to retire from Columbine at the end of this upcoming school year, where he has served as principal for 18 years. "My life was spared on that day."

DeAngelis described how two days after the Columbine shootings — in which 12 students and one teacher was shot to death before the two teen gunmen killed themselves in Littleton, Colo. — he went to his pastor seeking answers.

"He said, 'Frank, there's a reason you did not die that day. You got a cause. You need to rebuild that community.'"

On the morning of the shootings, DeAngelis was in his office. He steered about 20 students to safety, and survived with no physical injuries. But he has said the massacre left him with anxiety attacks so severe they felt like heart attacks — and contributed to the end of his marriage of 17 years.

"Anyone who walked back in that building at Columbine High School — any teacher, student, parent — had to re-live that day, day after day, as a constant reminder. So that took a lot of courage," DeAngelis told KUSA. "We'll never get back to normal. We had to redefine what normal is. But you can."

Slowly, the Columbine community started to heal, DeAngelis said.

"People just really feel that after a horrific event you're going to wake up some morning and everything's going to be back to what it was. It's never going to be. But that doesn't mean you give up hope. We moved forward," he said. "We cried together. We laughed together."

In the years since, DeAngelis has helped raise awareness nationwide of warning signs of violence in high school students, and this year, he was named Colorado Principal of the Year for 2012-2013 by the Colorado Association of School Executives.

DeAngelis had vowed to stay in his job until the students who were in kindergarten at the time of the shooting graduated from Columbine, KUSA reported. Those students graduated in 2011.

He said he felt like his career was "flashing before my eyes" as the pupils who had been students during the shooting grew up, and four or five of them became staff members at the high school.

"There is a bond, and it occurred on April 20th, that will be together forever," he said.

That bond was stronger than ever as news of DeAngelis' upcoming retirement spread through the Denver suburb.

Paula Reed, a long-time Columbine teacher, told NBC News through tears, "I don't know how to describe it except to say it's grief. We're going to miss him so tremendously."

Jason Webb, who has also taught at Columbine for years, said, "Frank's been equal parts protector, leader, and friend."

DeAngelis has been at Columbine for a total of 34 years, and worked as a teacher, coach, and assistant principal before he was promoted to principal.

"I get emotional thinking about that last graduation," DeAngelis told KUSA. "It's a great place. The only thing I hope is that it's a little bit better than when I first got there."

Principal Frank DeAngelis starts his final year at Columbine High School, where he helped shelter students during the infamous 1999 shooting spree. NBC News' Leanne Gregg reports.

NBC News' Leanne Gregg contributed to this story.