The documentary tells a story that's too good to be true.

"Unclaimed," by Canadian filmmaker Michael Jorgensen, is about a Vietnam veteran's search for and discovery of another Vietnam vet, a Birmingham native believed dead in 1968, who he believed was still alive and going about his life in Vietnam.

The amazing tale of Army Sgt. John Hartley Robertson's life in Vietnam, though, is likely more fiction than fact, according to reports Wednesday, a day after the film debuted at Toronto's Hot Docs film festival.

A 2009 memo from the U.S. Defense Prisoner of War/Missing Personnel Office sent to London's Daily Mail sheds light on the identity of the man who claims in the film to be Robertson. The newspaper reports he is a Vietnamese man of French origin named Dang Tan Ngoc.

The U.S. first became aware of Ngoc in 2006, when he reportedly claimed to be Robertson but recanted the claim under questioning the Daily Mail reported. He again claimed to be an American in 2008, but was fingerprinted at the U.S. Embassy and his prints did not match those of Robertson.

Officials said Ngoc has a history of pretending to be an American veteran, presumably to get money from tourists and veterans groups.

"I mean this guy was a frequent flier at our office," retired Lt. Col. Todd Emoto, who was the commander of the Joint Prisoner of War Accounting Command in Hanoi, Vietnam, from 2008 to 2010, told Business Insider. "It totally blows my mind that he's gotten this far. He forgot how to speak English and his kids' names? Who falls for that?"

Robertson's sister has said she believes the man she met in Canada in the film's climactic scene is her brother, and that she does not think DNA testing is necessary, the Daily Mail reported.

Jorgensen has said the film is really about the man who searched for Robertson, Tom Faunce, and that it makes no judgment about the truth of Robertson's identity, according to the Daily Mail.