For Dave Franco and Alison Brie, the real-life married couple who star in the horrifying “Together,” it’s never been more true to say, “The family that stays together, really, really stays together.”

For Franco’s Tim and Brie’s Millie, their new country house betokens a dangerous future once they fall into an abandoned cave in the nearby woods, drink from the underground pond and begin to change. To really get … together.

A hit at its Sundance premiere, “Together” sparked a $17 million bidding war.

It was natural for its stars, married since 2017, to play marrieds.

“This is actually our third time acting together,” Franco, 40, said in a joint virtual interview. “It’s our favorite thing, working together and I think our real relationship informed the relationship of the film.

“We’ve never worked this intensely together, where we were basically in every scene together, going home at the end of every day together. Spending  24 hours a day together.”

“We loved that we had the opportunity to ramp up to this,” Brie, 42, said. “It’s great being on set together. We trust each other more than anyone in the world and that enables us to take bigger risks in our performances.

“And this certainly was a big risk. We both were just blown away by the script and the horror set pieces were so wild and so unique.

“It excited us as actors to get to do things that we’ve never gotten to do before. It was like icing on the cake to do it together.”

As to what exactly body horror is?

“It’s when crazy (expletive) starts happening to your body. What’s so scary about body horror is that our bodies are our vessels,” Franco said, “we can’t escape. So when terrible things start to happen to us, it’s horrifying because you can’t hide from it.”

“Everybody,” Brie added, “has a complicated relationship with their body. And the body is changing until you die — and you are chained to it.

“The body horror genre is a fascinating way to explore any types of fears about your body. The visual language of body horror makes it very visceral.”

Like “The Substance,” Demi Moore’s Oscar-nominated body horror hit, “Together” is R-rated for its nudity.

“I’ve always been a bit of an exhibitionist,” Brie allowed. “To talk about body horror specifically, it makes sense that there are often scenes with nudity, because you’re dealing with the human body.

“Obviously, because we were shooting this together, it helped us have a level of comfortability on set that we might not normally have.

“You know,” she added without winking, “we’ve seen each other naked before.”

“Together” is in theaters today.