The U.S. Marine Corps stated Thursday that it had misidentified one of the Marines in the famous 1945 photo of six men raising the American flag at Iwo Jima.

An investigation conducted by the Marine Corps identified a man named Private First Class Harold Schultz who had never been associated with the photo before, and who had never claimed credit for his role, USA Today reports. Charles Neimeyer, a historian who served on the panel, states that Schulz’s refusal to reveal his role in the photo is a “mystery,” and that Schultz most likely “took his secret to the grave.”

Schultz joined the Marine Corps at the age of 17 and was seriously injured while serving in Iwo Jima. He later embarked on a 30-year career with the U.S. Postal Service. Schultz was engaged once after serving in World War II, but his fianceé died of a brain tumor before they wed. He eventually married at the age of 63, and was known for being “quiet and self-effacing.”

His stepdaughter, Dezreen MacDowell, said that her stepfather once confided to her that he was one of the Marines who had raised the flag in Iwo Jima. The two were eating dinner together in 1990 and discussing the war in the Pacific when he mentioned his role in the famous photograph, according to USA Today.

MacDowell recalls telling her stepfather, “Harold, you are a hero.”

He responded, “Not really. I was a Marine.”

Schultz died in 1995, long before two amateur historians who studied the photo began to speculate that Schultz might be pictured in the photo, which led to a Marine Corps investigation. But some close to him have claimed that Schultz did not want attention for his heroic deeds.

“He probably wouldn’t be really happy with us revealing this now,” Neimeyer said.