A rookie Bronx EMT, who went from the camaraderie of the FDNY academy directly into the horrors of the coronavirus pandemic, killed himself this week after less than three months on the job, police sources told The Post.

John Mondello, 23, used the gun registered to his father, a retired NYPD cop, to end his life Friday in Queens, the sources said.

His body was spotted by passersby at 6:48 p.m. at 25-40 Shore Blvd. in Astoria on the rocks along the river wall.

He was lying face up with the weapon still in his hand, a gunshot wound under his chin, witnesses said. The firearm was registered to the elder John Mondello, a retired cop, the sources said.

The younger Mondello graduated the Fire Department’s EMS Academy in early February, and went to work with the Tactical Response Group next to EMS Station 18 in Claremont — one of the busiest by 911 call volume in the city.

A friend and fellow graduate described him as “always very peppy, very happy.”

But a few weeks ago — at the apex of the Big Apple’s coronavirus crisis — Mondello reached out to his buddy, and said he didn’t like his new job, the pal recalled.

The Tactical Response Group runs non-stop to areas with the busiest emergency call volume in the city.

The fellow EMT assured Mondello “everything was going to get better,” and the two spoke about how “everyone feels stressed out and overwhelmed” and the notion that they got out of the academy and went “jumping into the pandemic, the high call volume.”

They discussed the “chaos” and how they were seeing “people passing away right in front of you. We don’t have the same union benefits as other city workers. It’s really stressful to work long hours and not get paid as much,” his pal added.

The heavy toll of coronavirus deaths weighed on Mondello, another friend told The Post.

“He told me he was experiencing a lot of anxiety witnessing a lot of death, he’d feel it was a heavy experience when he’d fail to save a life,” said Al Javier.

Anthony Almojera, vice president of the EMS officers’ union, said the devastation wrought by the virus is taking a toll on many of his crew members.

“This is indicative of what we’re all going through,” he said. “Hopefully people will reach out when they need help and don’t resort to this type of action. There are places to go if people need help.”

The FDNY offers and has been promoting mental health counseling to all members during the pandemic.

“The loss of this young EMT who chose to bravely serve others is a tragedy for our entire department. We all mourn his loss and our prayers are with his family,” FDNY Commissioner Daniel Nigro said.

Relatives were shattered.

“He’s a wonderful boy and they’re a wonderful family,” a relative said Saturday. “We are totally devastated. Beautiful personality. Big heart.”

The Queens native went to La Guardia Community College, and then on to St. John’s University, according to his Facebook page.

Before becoming an EMT, Mondello made ends meet delivering food for the K&L deli in Jackson Heights, from November 2015 until March 2016.

“He was always smiling, always joking around. He never seemed upset,” store manager Peter Lee said.

The FDNY football team tweeted “RIP EMT John Mondello” on Saturday, alongside a photo of the rookie, wearing his crisply pressed uniform, a wide smile across his face.