Spoiler alert: This post contains spoilers from “The Farewell”

The tagline from director Lulu Wang’s comedy/drama “The Farewell” hints at its real-life inspiration: “Based on an actual lie.”

The plot revolves around Billi (Awkwafina) and her family’s decision to not inform Nai Nai — the Chinese word for grandmother — about her terminal cancer diagnosis. They believe that telling Nai Nai the truth will only accelerate her demise.

So the family concocts and elaborate scheme, including doctoring medical reports and throwing an impromptu wedding in China, to keep Nai Nai’s spirts, and hopefully health, up. Billi struggles with whether or not to reveal the secret, and in the end returns to New York maintaining the lie, expecting to never see her grandmother again.

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But that’s not the end of the story.

The very last scene in “The Farewell” is a shot of Wang’s real-life grandma, and a caption that reads “Six years after her diagnosis, Nai Nai is still with us.”

Wang based “The Farewell” on her own family’s actual lie — one that hasn’t been revealed to her grandma after all this time. But now with the film getting widespread press coverage and even distribution in China, Wang is terrified that her Nai Nai will not only discover her cancer diagnosis but the fact an entire film has been made about her.

“It’s really playing with fire,” Wang said during a Q&A at a recent screening. When asked if she was worried that her grandma would find out, Wang replied, “Oh yeah, every day.”

“There’ve been articles everywhere,” Wang explained. “The New York Times has been translated into Chinese, we screened at the Shanghai Film Festival, we have a Chinese distributor, they’re cutting the trailer in Chinese.”

“We’ve been punting this problem down the line and now it’s going to be released. I don’t want grandma to find out on the television when the commercial comes up,” she added, half-jokingly. “That would be a very bad way to find out about all of this. Not only have we been lying to her about what the movie is about, but we’ve been lying to her the last six years. That my cousin got married because she was sick.”

But there was an even bigger problem on set. Wang’s grandma came to visit while production was underway in Changchun, just down the street from where she resides.

“I told the crew — they’re local and Chinese and they knew — ‘please don’t tell my grandma,'” Wang said.

Even if the crew didn’t spill the beans, their clothes almost did.

“At the time we didn’t have a title, so the company was just called Nai Nai,” Wang explained. “All of the production vehicles had signs that said Nai Nai in Chinese characters. And then the producers got production start gifts for the crew, and they were t-shirts that said Nai Nai. And they were handing them around on set.”

“I got to set and was literally like, ‘What are you guys doing? We’re literally a block from my grandma’s house,'” she recalled. “The first thing I did was confiscate all the t-shirts!”

And then there was the issue of casting her own aunt — affectionately dubbed Little Nai Nai — in the film.

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In real life, Little Nai Nai serves as grandma’s caretaker, and Wang had to explain her absence.

“I was like, ‘Sorry, little Nai Nai can’t take care of you for a month because I want her to be in my movie,'” Wang recounts telling her grandma. When asked by her grandma who Little Nai Nai was portraying, Wang quickly answered, “Uh, an old lady.”

“Eventually we told her it’s based loosely on our family; it’s about our family who lives in America and going back to China for a reunion because of a wedding,” she added. But for now, grandma remains in the dark.

When she eventually finds out, Little Nai Nai already has an explanation prepared.

“I think we’ll just say movies are fictional,” she recommends.

Sounds good to us.

“The Farewell” opens wide on August 2.