Patrick Schwarzenegger Reveals How Brother-in-Law Chris Pratt Helped Him Prep for The Terminal List

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Patrick Schwarzenegger's latest project is a family affair!

While appearing on Jimmy Kimmel Live Wednesday, the 28-year-old actor chatted with guest host Sean Hayes about how his brother-in-law, Chris Pratt helped him get into character for The Terminal List. Pratt, 43, stars in and produces the upcoming eight-episode Amazon Prime Video series, in which a Navy SEAL officer investigates why his entire platoon was ambushed during a covert mission.

"I remember when Chris said, 'Hey you know there's this young role, Donny Mitchell, you'll be the youngest in the platoon. But if you want to get this role, I need you to go and try to get into character and really get this,' " Schwarzenegger explained.

"I need you to gain 20 lbs. and start tactical training, and know how they move, the body language, all this stuff,'" he continued. "So it was kind of like a dream come true to get to work with them and learn from them," Schwarzenegger added of the "insane" experience of training with real-life SEALs.

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"And you know, I have such pride in our country and the men and women in our armed forces," The Staircase star said. "To get to kind of work with them and work beside them in the actual show – I would say 80, 90 percent of the actual actors in The Terminal List were real Navy SEALS – it was a really cool experience."

Based on the bestselling novel by Jack Carr, writer, showrunner and executive producer David DiGilio told PEOPLE his team hopes The Terminal List is the biggest hit of the summer.

"Jack's mixture of action, conspiracy, and military authenticity is unparalleled on the page. We knew that if we honored that authenticity, and added in some hair-raising psychological twists and turns, we would have something not just entertaining, but wholly original onscreen," DiGilio said of the adaptation. "We've taken all of Jack Carr's tradecraft and set it against a tone of paranoia and intrigue."

The project marks the first time that Schwarzenegger will act alongside his brother-in-law. Pratt is married to Patrick's sister Katherine Schwarzenegger, with whom he shares daughters Lyla Maria, 22 months, and new baby Eloise, born in May. Pratt is also dad to son Jack, 9½, with ex-wife Anna Faris.

On the red carpet for his new movie The Terminal List on Wednesday, the Guardians of the Galaxy star gushed about his newborn daughter even amid some sleepless nights.

Chris Pratt and Katherine Schwarenegger
Chris Pratt and Katherine Schwarenegger

Chris Pratt/Instagram

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"She's perfect, she's so gorgeous," Pratt told Entertainment Tonight of Eloise. "She's so chill, she sleeps a lot during the day. At night, not so much, so I am working on some caffeine fumes right now. But she's perfect."

As for big brother Jack, Pratt added that he "does a great job as a big brother" to his sisters.

"There's a big age separation... [and] he does a great job, he's so sweet with them," he told ET. "And they love him so much and they miss him when he's gone."

The Terminal List premieres on Prime Video July 1.