The list of heroes immortalized in the iconic photo of the U.S. flag being raised over Iwo Jima has been revised again.

The Marine Corps acknowledged on Wednesday that for 74 years, it had misidentified one of the six fighting men who appeared in the Pulitzer Prize-winning photograph by Associated Press photographer Joe Rosenthal.

The admission came after three historians, using film footage from atop Mount Suribachi and photos taken by other soldiers who were there, concluded that Cpl. Harold “Pie” Keller — not Pfc. Rene Gagnon — was one of the flag-raisers in the photograph.

The findings of historians Stephen Foley, Dustin Spence and Brent Westemeyer were confirmed by a special investigative board convened by the Marines and by investigators from the FBI's Digital Evidence Laboratory.

"Without the initiative and contributions of both private historians devoted to preservation of our history and the FBI’s Digital Evidence Laboratory, the Marine Corps would not have this opportunity to expand on the historical record of the second flag raising on Mount Suribachi," the Marine Corps said in a statement.

The addition of Keller's name comes three years after an earlier Marine Corps inquiry concluded that Pfc. Harold Schultz was one of the six flag-raisers, not Navy hospital corpsman John Bradley as had been believed for seven decades.

Wartime photo of Corp. Harold Keller. Courtesy of Keller family

"Regardless of who was in the photograph, each and every Marine who set foot on Iwo Jima, or supported the effort from the sea and air around the island is, and always will be, a part of our Corps’ cherished history," the Marines' statement read. "In the words of General David H. Berger, Commandant of the Marine Corps, 'they are all heroes.'”

The discovery that Keller, a Purple Heart recipient who fought in the biggest battles of the Pacific theater, was in the Rosenthal photo came as a shock to his family in Brooklyn, Iowa.

“He never spoke about any of this when we were growing up,” Keller’s daughter, Kay Maurer, 70, told NBC News. “We knew he fought in the war, we knew he was wounded in the shoulder at one point...But he didn’t tell us he helped raise the flag on Mount Suribachi.”

There was evidence Keller was there hanging in plain sight on the family’s living room wall — a framed photo of another renowned Rosenthal photo from Feb. 23, 1945, the so-called Gung Ho shot of 18 Marines on the summit with the flag in the background, Maurer said.

“Now we know he’s in that photo, too,” Maurer said of her father, who got his nickname after he ate too much pie before a football game and threw up in front of his friends. “When I would ask him about the photo on our wall, he would say something like, ‘That group raised a flag.’ He just never spoke much about this when we were growing up.”

Keller and Gagnon both died of heart attacks in 1979. Keller was 57 and there was no mention of Iwo Jima in his obituary. Gagnon was 54 when he died seven months later and is buried in Arlington National Cemetery. His obituary on the cemetery site refers to him as an "Iwo Jima Flag Raiser."

There were actually two Iwo Jima flag-raisings on on Feb. 23, 1945, to signal that one of the bloodiest battles of World War II would soon be won. The first flag was deemed too small by military brass and replaced a few hours after it went up with a second, larger flag. Rosenthal's prize-wining picture was of the second flag-raising.

Mount Suribachi, Japan on Feb. 23, 1945. Pvt. George Burns / U.S. Army / Courtesy U.S. Army Heritage and Education Center

"Private First Class Gagnon played a significant role in the flag raising on Mount Suribachi and his role will never be diminished," the Marines said in a statement. "He was directly responsible for getting the larger second flag to the top and returning the first flag for safe keeping. Without his efforts, this historical event might not have been captured, let alone even occurred."

Spence, Foley and Westmeyer are military historians who have long had a keen interest in Iwo Jima and what happened there.

Foley, who is Irish, was one of the two historians who worked on confirming that Schultz was in the Rosenthal photo, not Bradley. Bradley was the subject of the bestseller “Flags of Our Fathers,” which was written by his son, James Bradley. It was later turned into a movie by Clint Eastwood.

Maurer said Westemeyer had long harbored suspicions that Gagnon was not one of the six flag raisers. “The first time he thought it might be my dad was because of his stature,” she said.

Keller was a strapping, square-jawed Marine while Gagnon was more slender and had a distinctive mole on this face, Westemeyer said.

Westemeyer's suspicions hardened into certainty in 2014 after he immersed himself in the film footage that was taken on the summit by Sgt. Bill Genaust, a Marine cameraman who was killed in action a week later.

“After watching Genaust’s footage a thousand times over, I was a 100 percent certain Gagnon was not in the number two position,” Westemeyer said.

Westemeyer was referring to the position of the men who appear in the Rosenthal photo, which until Wednesday was, from left to right, Ira Hayes, Schultz, Michael Strank, Franklin Sousley, Gagnon and Harlon Block.

Of the six figures in the photo, the man in the position second from the right is the most obscured in Rosenthal’s photo.

Westemeyer, who lives in Iowa, said he shared his belief with Foley via an Iwo Jima forum to which they both belonged. Foley, in turn, had been in contact with the California-based Spence.

“I started peppering Steve, ‘It’s Harold ‘Pie’ Keller,’” Westemeyer said.

Moments after the second flag has been raised. Lt. Harold G. Schrier salutes on the left and Plat. Sgt. Ernest I. Thomas Jr. on the right. Pvt. Campbell / NARA

They compared stills from Genaust’s footage with photographs of the scene taken from different vantage points by other photographers who were there, including Army Pft. George Burns. Spence tracked down the Burns photographs at Foley's urging and after reading an NBC News article in 2016 about Burns and another forgotten military photographer, Marine Sgt. Louis Burmeister.

Foley then tracked down a photograph in 2017 taken by Marine Pvt. Bob Campbell, which showed two men saluting as the six men are raising the flag.

Also, a closer look at Rosenthal’s prize-winning photo revealed what appeared to be the “reflection of a ring” on the left hand of the man in the second spot, Spence said.

“Keller was married, Gagnon wasn’t,” Spence said.

In fact, Keller met and married his wife, Ruby, in a “whirlwind romance” while home on leave in February 1944, Spence said.

There were other clues in the photographs they collected, Spence said, like the camouflage pattern and creases on Keller’s helmet matching that of the man in the second spot.

But it was a Campbell photo that shows Gagnon, with his telltale mole visible, reaching for the first flag while Keller and the others are raising the second flag on the summit that sealed it for the historians.

"Campbell's Exchange photo was made public many, many moons ago," Westemeyer said. "We simply did not focus on who was lowering number one."

Keller was slated to go to officer training school at Quantico, Virginia, when the war ended and he decided, instead, to go home. He returned to his job as a telephone lineman and raised two sons and his daughter, Kay.

Pvt. Bob Campbell's shot of the first flag being lowered as the second is raised. Pvt. Bob Campbell / NARA

“I think he just came home and wanted to put it all behind him,” Maurer said. “Just carry on.”

Maurer could recall only a couple of other tidbits from the war that his father told her.

“Once he told me what jungle rot was,” she said. “The other thing we knew about was that he got to see Eleanor Roosevelt when she visited the troops.”

Maurer said she learned from her mother that her father had nightmares from time to time when he first came home from the war. She said that, in time, they stopped. But habits her father picked up in the service stuck with him.

“When he ate, he would always leave a little food on his plate,” Maurer said. “We were always told to clean our plates but he never did. Finally I asked him why and he said: ‘When I was in the war, we weren’t always sure when we would get our rations. So I would save a bit. I can’t break that habit now.’”