Two former firefighters who heroically responded to the 9/11 terror attacks in New York City have died due to illnesses related to that fateful day, according to the Uniformed Firefighters Association.

The group announced on Sunday that firefighter Thomas Dunn of Engine 234 in Brooklyn passed away from a World Trade Center-related illness.

The news came just three days after retired Battalion Chief Dennis Collopy died on Jan. 30 from cancer, related to his rescue efforts.

Firefighter Thomas Dunn, left, and Retired Battalion Chief Dennis Collopy, right, have died from illnesses related to 9/11. (Uniformed Firefighters Association and Porter Gifford, Getty, background.)

Others thanked him for his service and his heroic reactions at the World Trade Center on Sept. 11, 2001, when Al-Qaeda terrorists flew hijacked planes into the Twin Towers, killing nearly 3,000 people, including 343 firefighters. 

Retired Battalion Chief Dennis Collopy died after “a courageous battle with cancer,” according to his obituary.

He was a 36-year FDNY veteran and a U.S. Army veteran, the Uniformed Firefighters Association said. 

Collopy is survived by his wife of 60 years, his two daughters and four grandsons.   

A Bronx native, he later lived in West Nyack, in upstate New York. He worked for the FDNY until he retired in 2002.

“A truly great man, blessed that I had the honor of knowing him. RIP. Brother,” John Murphy wrote on a Facebook firefighter group.

“RIP Chief, thank you for your service to country, and community,” wrote Michael Richard. “Thank you for your ultimate sacrifice. Hooah. Your tour’s over. Rest easy.”

Collopy’s funeral mass is being held on Tuesday in West Nyack.

FDNY firefighters carry fellow firefighter, Al Fuentes, who was injured in the collapse of the World Trade Center on Sept. 11, 2001.  ( Matt Moyer/Corbis via Getty Images)

More than 370 firefighters died after the attacks due to 9/11-related illnesses, which include liver cancer and laryngeal cancer. Other illnesses first responders suffered include Mesothelioma, musculoskeletal disorders, chronic rhinosinusitis, gastroesophageal reflux disease (GERD), asthma, sleep apnea, other cancers, posttraumatic stress disorder (PTSD) and chronic respiratory disease.

The collapse of the towers in Manhattan created a massive dust cloud, consisting of pulverized building materials, asbestos, silica, metals and concrete that blanketed the World Trade Center site and the surrounding area.