"Oh yeah," said Gubish, the weathered image sparking his recollection. "That was my buddy, Gray."
Harry Gray died 75 years ago, fighting for his country on a remote, volcanic island thousands of miles from home. He's a person who MacCallum never met, but whose story she knows well.
"He was my uncle," said MacCallum, visibly holding back her emotions.
The incredible scene was the culmination of years of research that MacCallum spent closing the circle on a family story that had been passed down generations, but had never been fully completed until now.
This is all told in MacCallum's new book, "Unknown Valor: A Story of Family, Courage and Sacrifice from Pearl Harbor to Iwo Jima," and in associated Fox News and Fox Nation specials.
"In war movies there are the heroes and then there are hundreds of others," said MacCallum in the Fox Nation show. "The guys who get hit on the beach or in the villages, just trying to carry out the mission. ... They are the 'extras' in the movie, but for some family somewhere, they are their 'Harry Gray.' ... the line on the family tree that just ends, a young man who never got to have a life, get married, grow old."
MacCallum began learning about her mother's cousin, Harry, when she was a young girl.
He was 18 years old in the summer of 1944, when he left Arlington, Mass., to join the Marines and fight in World War II.
Harry and nearly 7,000 fellow Marines were killed fighting on Iwo Jima, in what would prove to be one of the bloodiest battles of the war, as the U.S. military prepared for an invasion of Imperial Japan.
"As allied forces fought the Nazis in Europe," narrated MacCallum, "America was virtually alone in the battle against the Japanese in the Pacific."
For MacCallum's family, all they knew of the fate of their son, brother and cousin, was what they could glean from letters and official reports -- that he was killed on Iwo Jima on March 13, 1945.
After returning from a trip to Iwo Jima, retracing her uncle's footsteps, MacCallum received a tip that would lead to a series of incredible discoveries.
"I got a call from a researcher friend," said MacCallum in the Fox Nation piece. "He asked for a picture of Harry Gray to show his friend, Charlie Gubish. We knew Charlie was in the 34th replacement draft and had also been wounded on March 13."
"He was my buddy," Gubish told MacCallum as they sat across from each other in one remarkable scene. "My foxhole buddy. He’d always call me 'Pop' because I was 24 at that time and he was 18. He’d always say, 'Pop, sleep, I’ll watch.'"
"To find Charlies after all these years was not something I had ever anticipated," said MacCallum, reflecting on that interview. "His story lined up perfectly with everything we knew about that day and he was able to tell us things about Harry we would never have known."
Gubish remembered the day that Harry was killed, as they marched to the front for the very first time, providing the only first-hand account of his death.
"A mortar shell landed on the right-hand side, about 50 feet and nobody paid no attention," said Gubish. "Then there was one on the left-hand side, about the same distance. I hollered, hit the deck. They got us right in the middle. Well, that’s what killed him."
As MacCallum neared finishing her book, she decided to make another attempt at tracking down more close acquaintances of her uncle, and again, it paid off.
She located Harry's friend, George Colburn, who had also enlisted in the Marines and lived in nearby Medford, Mass.
"George was alive at 93 years old!" said MacCallum in the Fox Nation special. "The same age as his old buddy, Harry Gray."
"When George and I connected, I told him that I was Harry Gray's niece. He wept and told me he thought about Harry all the time."
In fact, it was one of George's letters to Harry's parents that gave the family its first insights into his sacrifice.
"Dear Mrs. Gray," Colburn wrote in the decades-old letter. "This is about the 5th letter I've started. I can't seem to put into writing just what I wanted to say. Harry and I were great buddies. ... I was with him up on Iwo Jima. I was with him the day it happened. I'm sure he was killed instantly and there was no pain. ... I'm sure he went to Heaven. He was a brave kid."
When MacCallum spoke to Colburn on camera he could not contain his grief -- still raw after 75 years.
"That was March 13, I think, because that’s the night that we had an awful mortar attack," he told MacCallum. "One of them landed right between Harry and the kid next to him. Killed both of them. He never cried out. So I knew, he died instantly."
"And I go down the line," he said, remembering the words of fellow Marines. "'Hey, your buddy got killed.' 'I know, I know, I know, I know.'"
"His body was over there," Colburn said, his voice choked with emotion. "I went over and I wanted to kick him, like, 'Why did you do this? Don’t you know I love ya?' And I never saw him again."
To watch all of "Unknown Valor: A Story of Family, Courage, and Sacrifice," visit Fox Nation and sign up today.
Fox Nation programs are viewable on-demand and from your mobile device app, but only for Fox Nation subscribers. Go to Fox Nation to start a free trial and watch the extensive library from Tomi Lahren, Pete Hegseth, Abby Hornacek, Laura Ingraham, Ainsley Earhardt, Greg Gutfeld, Judge Andrew Napolitano and many more of your favorite Fox News personalities.