A beloved former FDNY fire marshal has died from the coronavirus, sources and union officials said Monday.

John Knox, 84, succumbed to the deadly disease following a weekslong battle, sources told The Post and the FDNY-Uniformed Firefighters Association confirmed.

The retired Bravest, a Queens resident, had been hospitalized at Mount Sinai South Nassau hospital in Oceanside, Long Island since Feb. 26, when he felt dizzy and experienced bouts of coughing and vomiting, his son, Zachary, previously told The Post.

Because he hadn’t traveled to any high-risk countries or crossed paths with those who had, doctors didn’t test for the COVID-19 until March 9, according to his son.

The diagnosis came back Friday, after Knox had been heavily sedated and breathing with the help of a ventilator for 10 days.

His family had hoped that he would be eligible for an experimental course of Remdesivir, an unapproved drug used in experiments to fight Ebola, but he didn’t qualify due to his acute kidney failure.

Prior to joining the Bravest, Knox spent two years with the NYPD and served with the Marines in Korea.

A photo of Knox in the military.
A photo of Knox in the military.

He then served with the FDNY from 1960 through 1998, spending 34 of those years as a fire marshal.

Knox is survived by his wife, three daughters and six grandkids.

“Our sympathies and prayers go out to the Knox family during this especially difficult time, following the tragic loss of their beloved husband, father, and grandfather,” said FDNY-Firefighters Association President Gerard Fitzgerald.

“John was a proud Fire Marshal Representative in the Uniformed Firefighters Association and served this department and his fellow Fire Marshals for many years,” he continued. “We are thankful for the memories and are grateful for his service to this City and this Union.”

It was not immediately clear when Knox succumbed, and whether his passing represented the seventh statewide death announced by Gov. Andrew Cuomo early Monday or an eighth.