13-Year-Old Boy Battling Cancer Sworn In as Sheriff's Deputy: 'It Was The Best Day Of His Life'

Julian Cardenas has struggled to keep his spirits up as he battles leukemia.

At the tender age of 13, Julian Cardenas has already endured an adult-sized heap of pain and despair.

He was diagnosed with cancer in February and was immediately slammed into a terrifying new world filled with needles, chemotherapy, doctors, nurses, and prolonged, isolated hospital stays.

Read: Girl, 14, With Spinal Muscular Atrophy Decides To End Her Life: 'This Is Enough Pain'

On one day recently, it all became too much. Overwhelmed by fear, Julian suffered a massive panic attack. He couldn’t breathe, and he didn’t think he could go on living this way. He was just a boy, and he wanted to go outside and play with his friends.

His family dialed 911. And that was how he crossed paths with Los Angeles County Sheriff’s Det. Marianne Oliver and how he came to be a L.A. Sheriff's deputy — for one fun-filled day.

On Wednesday, Julian was sworn into the department with much fanfare. He flew in a helicopter. He drove a fire truck (from the steering wheel in the back), he learned how to fire a weapon and he rode around with a SWAT team.

“He said it was the best day of his life,” Oliver told InsideEdition.com.

She set Wednesday’s festivities in motion after responding to the Cardenas family’s emergency call.

“He was a little stressed out. He was despondent. He was depressed that he couldn’t go out with his friends,” Oliver said.  After calming Julian, and on her way back to the station, Oliver began to think of her nephew, who also had leukemia around the same age as Julian.

She went to her boss and told him about the boy. “I said, ‘Can I take him for a ride in a squad car around here? I wanted to do something for him. I wanted to cheer him up.”

Her captain "did that and much more. He arranged helicopters, the fire department, he arranged the SWAT team to come out. That is the type of person he is. “

Julian had a blast, she said. Aboard a sheriff’s helicopter, Julian was flown over his house, his school, Dodger Stadium and Hollywood.

Read: Boy With Leukemia Sworn In As K9 Handler, One Day Before He Begins 3-Year Treatment

At the end of the day there was a community BBQ and residents donated money to him — about $1,000. “He was thrilled,” Oliver said. “For a 13-year-old kid?  That’s a lot of money.”

On Thursday, Julian was back in Children’s Hospital of Orange County, where he’ll spend the next few days undergoing bone marrow treatment. Because his immune system is compromised, he must be kept in isolation to prevent him from catching someone’s cold or cough.

But he’s still jabbering away about his brief career as a Sheriff’s deputy, his oldest sister said.

“He was shocked by how much they did,” said Odalys Cardenas. “He’d never flown before. It made his day, it made his year, it made his summer. He was really happy.”

Watch: Firefighters Give 6-Year-Old Hero's Farewell After Losing Battle With Cancer