'This Is Us' star filming flashbacks in Vietnam

“This Is Us” star Milo Ventimiglia was between scenes on the set in Vietnam, the setting for a critical flashback story about his character Jack's wartime tragedy.

Then modern-day reality merged with TV fiction.

“I'm there in full battle dress, my rifle slung, my hat on, looking very much the 1970 U.S. soldier, and an older gentleman going past us said something in Vietnamese, did a double-take on me and then just kept going,” Ventimiglia said of last month's encounter outside Ho Chi Minh City.

The Vietnamese actors he was working with burst out laughing, then filled him in.

“What the hell? What the hell is a U.S. soldier doing back here?” the man exclaimed as he zipped by on a motor scooter, Ventimiglia was told.

It was an isolated blip in an otherwise smooth week of shooting in Vietnam, with the scenes to be scattered throughout “This Is Us” episodes as the series unravels a key chapter of Jack's life.

The NBC drama, which toggles back and forth in time, is zeroing in on what Jack endured during the war: The death of his brother, Nicky, played by Michael Angarano.

But unlike the prolonged, angst-building revelation of how family man Jack died, series creator Dan Fogelman said the circumstances of Nicky's fate will be known by this season's end.

Fogelman said the importance of the story line, and the lack of a military veteran on the show's writing staff, warranted bringing in Vietnam veteran and acclaimed writer Tim O'Brien (“The Things They Carried”) as a consultant.

O'Brien said he's been impressed by the show's approach and its artistry.

“They're just totally committed to making getting everything right,” he said, in contrast to many other Vietnam dramas. “But even more important to me was the quality of the show. ... They seem so committed to making a beautiful show that touches on human pain and struggle and human joy.”