A fourth firefighter has died from injuries sustained during a burnover while battling the Knowles Fire in western Colorado last month.

Nathan Matthews, 43, of Lincoln, Nebraska, died July 24 from burn injuries he suffered during the June 27 incident, according to the U.S. Department of the Interior.

Matthews, a member of the Wildland Fire Service assigned to the Rifle Helitack crew, was one of five firefighters caught in the burnover while conducting initial operations on the fire.

Three firefighters — Emily Barker, 38, of Clinton Township, Michigan; Nick Hutcherson, 27, of Glendale, Arizona; and Sydney Watson, 27, of Warrior, Alabama — died at the scene.

Matthews had been receiving medical care since the incident.

“This is another heartbreaking loss for our wildland fire family,” U.S. Wildland Fire Service Chief Brian Fennessy said in a statement. “We mourn the loss of Nate while continuing to grieve the deaths of Emily, Nick and Sydney. Our hearts are with their families, friends, crewmates and everyone impacted by this tragedy.”

Fennessy said the agency remains committed to supporting those affected and honoring the legacy of the four firefighters.

A serious accident investigation team continues to review the circumstances surrounding the burnover, according to federal officials.

Gov. Jared Polis also issued a statement mourning Matthews’ death. Matthews was injured while responding to the Knowles Fire, which later became the Snyder Fire.

“I’m so saddened by the loss of Nathan Matthews,” Polis said. “His bravery, and the bravery of his colleagues, is the reason that so many of our homes, communities and lands have been protected from the fires over the course of this season.”

Polis said the state would lower flags to half-staff on the day of Matthews’ memorial service, which has not yet been announced.

“My heart is with Nathan’s family and his colleagues, many who are still mourning the loss of Emily, Nick and Sydney,” Polis said. “And to all the firefighters who continue working day and night to protect our state, you have our immense gratitude.”

Information regarding memorial services for Matthews will be released at a later date, federal officials said.