Brendan Bialy, the aspiring Marine who jumped into action during the Colorado school shooting, said he desperately pumped the chest of his fallen friend after they tackled one of the attackers.

Despite his efforts, 18-year-old Kendrick Castillo died after throwing himself on the shooter at STEM School Highlands Ranch on Tuesday.

Another heroic student, Joshua Jones, suffered two gunshot wounds during the scuffle and is recovering at home.

Bialy, 18, told a packed news conference Wednesday that he felt “absolute fear” at first — but then rushed to help his two classmates subdue the shooter in their 12th-grade English class, according to the Denver Post.

“I don’t like the idea of running and hiding,” he said. “Kendrick Castillo died a legend. He died a trouper. He got his ticket to Valhalla, and I know he will be with me for the rest of my life.”

Castillo reacted with no hesitation, lunging at the shooter “like a bowling ball,” he said.

“The gunman was there, then he was against the wall, and he didn’t know what the hell hit him,” said Bialy, who managed to dislodge the shooter’s gun after he got off a couple of shots.

Bialy said he personally knew the attacker, but declined to identify which of the two STEM School shooting suspects it was.

The young man, who joined the Marine Corps Delayed Entry Program, is scheduled to report to recruit training this summer.

“At the end of the day, the reason I joined is to help people,” he said. “And I’m going to do that.”

But he said he feels uncomfortable being called a hero and attributed his bravery to his parents, who were seated at his side.

“It must be the genetics,” he quipped, adding that he was thankful to have emerged unscathed from the ordeal.

“I was blessed by something,” he said. “Somebody watching down on me.”

Bialy said he appreciates the support he’s received on social media, as well as messages from service members in the Marines, Army, Navy and Air Force thanking him for his service.

“But every time I hear something like that, I need to let them know that Kendrick Castillo and the other student were in the thick of it on rolling on the ground where I was too,” Bialy said.

He again reminded reporters about Castillo’s sacrifice.

“Kendrick was a total nerd,” Bialy said, smiling. “He was a fantastic, wholesome person.”

He repeated his Instagram motto: “I refuse to be a victim.”

“Why in the world would I let this coward get what he wants? I’m not a victim,” he said. “I refuse to be a victim. Kendrick refused to be a victim.”