1883 's Faith Hill, Tim McGraw: How They Make Sure Their Real Marriage Is Different Than the Show

Faith Hill and Tim McGraw have faced plenty of challenges in the four months since they began filming on location in Montana and Texas for 1883, the upcoming prequel series to Yellowstone: rattlesnakes, fields strewn with cow patties, sweltering Texas heat — and the complexities of bathroom breaks while wearing corsets and petticoats.

"There's just so many layers of clothing," Hill says. "Sometimes you're successful and sometimes you're not."

But for Hill, the most difficult moment was a quiet day on set shooting a scene where the characters that she and her husband portray, James and Margaret Dutton (great-grandparents to Yellowstone patriarch John Dutton, played by Kevin Costner), take a bath together.

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"It was really uncomfortable for me personally because I'm a very shy person in that type of situation," Hill, 54, tells PEOPLE in this week's cover story, on stands this Friday. "I obviously feel comfortable with my husband, but this is different. For intimate scenes, I feel like that belongs to us."

Jim Wright Faith Hill and Tim McGraw on the cover of PEOPLE

Series creator Taylor Sheridan, who recruited McGraw, 54, to play the elder Dutton in a Yellowstone flashback in the season four opener before developing the stand-alone series (premiering Dec. 19 on Paramount +), closed the set the day of the bathtub scene — "and it turned out to be beautiful," Hill says.

But it was just one instance of how the country stars had to navigate the separation between their real-life marriage and the couple they play on the show, which tells the story of how the Dutton family made the journey on a wagon train to Montana and amassed the land that became Yellowstone Ranch.

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Although each has acted before — McGraw made his major film debut in 2004's Friday Night Lights and has gone on to appear in eight other films including the Oscar-winning The Blind Side, while Hill has starred in 2004's Stepford Wives and 2017's Dixieland — the project marks the first time the pair have acted together. They decided they needed to set up some ground rules for the work.

"We have made it a point not to work on our scenes together until we're on set," Hill says. "It's important that we react to one another naturally as characters, not as husband and wife."

Watch the full episode People Cover Story: Tim McGraw & Faith Hill on PeopleTV.com or on the PeopleTV app.

The couple marked their 25th wedding anniversary on Oct. 6 while filming the show.

"I was hauling ass in a carriage through a river," Hill says. "That was our big celebration!"

Jim Wright Faith Hill and Tim McGraw

And that's just the way they wanted it, says McGraw: "It's been incredible to do scenes together and to watch her work."

Even, he adds, when the acting seemed to hit a little close to home. "We had this scene where she has to slap me. I was expecting a finger slap but it was a paw to the jaw. There was 25 years of pent-up aggression going on!" McGraw jokes. "When you see it on screen, you realize it was a genuine hit."

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Joking aside, the couple, empty nesters now that their three daughters (Gracie, 24, Maggie, 23 and Audrey, 20) have all moved out of their Nashville home and are pursuing their own careers, say working on the project together has been a joy.

"I've never had so much fun in my life," McGraw says. Adds Hill, "I don't want to stop."

1883 premieres Dec. 19 on Paramount +.