(ABC News) -- Five weeks after the worst day of his young life, Brendan McDonough still hears the cell phones that were ringing in the back of his fire truck, the agonizing peal of loved ones desperate to reach his 19 missing buddies in the Granite Mountain Interagency Hotshot Crew fighting a raging wildfire on a scorched Arizona mountainside.
"Whoever didn't bring their phone, I could hear phones ringing, knowing that it was their wives, their family," McDonough recounted in an exclusive interview with ABC News to air on "Good Morning America" today. Additional portions will be broadcast tonight on "World News With Diane Sawyer" and "Nightline".
But by then the 21-year-old elite wildland firefighter -- whom his fellow Hotshots affectionately called "Donut" in a play on his last name -- knew the horrible truth that their own families did not yet know, as he sat in the seat absorbing the magnitude of what was happening.
All 19 of his brother Hotshots had just been killed by the ripping Yarnell Hill blaze in the largest loss of life among firefighters since the 9/11 attacks.
"I sunk. Sunk into my seat, I sunk into myself," he said in the ABC News interview, finally breaking his silence over how the terrible incident unfolded, in which only he survived.
Every one of the Granite Mountain Hotshots, except for McDonough, was burned alive sometime after 4:30 p.m. on June 30, when the Yarnell Hill Fire suddenly whipped 180 degrees around and cut off their escape route from a scrub brush meadow to a nearby ranch.
Almost two hours after it was reported at 4:47 p.m. that the Hotshots had deployed protective personal shelters, an Arizona state paramedic hiked up to the site of torched chaparral and confirmed the worst.
McDonough survived simply because he'd been chosen that day for an important job -- he was the crew's lookout a half mile away watching "fire behavior" and monitoring weather changes -- and he was able to escape the cascade of flames shooting as high as 50 feet.
Inside the Granite Mountain Hotshots' station house in Prescott, in his first visit only weeks after the catastrophic loss, McDonough felt at ease -- enough to reveal his deep pain over not being with his friends, who were all like family to him, when they died in their boots.
"I asked a million times, 'Why am I sitting here and why isn't someone else? Why aren't they sitting here with me?'" McDonough said.
Covered in soot over his bright yellow protective clothing and heavy boots as darkness fell on June 30, waves of guilt for being the only Hotshot spared death was a gut punch made all the more painful by the chirping phones behind him in the buggy.
Days later, he had a tattoo artist ink the stanzas of an old Gaelic prayer inside his right bicep as a constant reminder of his hope that the fallen "Nineteen," as they're now known in Prescott, have found peace.