Jennifer Garner and Her Stunt Double Dish About Their Longtime Friendship (Exclusive)

ET spoke with Garner and her longtime stunt double, Shauna Duggins, while promoting their new film, 'Peppermint,' in theaters Sept. 7.

For Jennifer Garner's upcoming action revenge thriller Peppermint, the former Alias star racks up a serious body count as she blasts her way through a legion of bad guys. But, to get into peak combat form, Garner got a little help from her longtime stunt double, Shauna Duggins.

ET's Kevin Frazier spoke with Garner on Friday, while promoting her upcoming thriller, where they were joined by Duggins who dished on the film's intense fight sequences and her bond with Garner.

The actress said that Duggins, who is one of her "closest friends," pushed her to get into the headspace she needed to throw a punch or shoot a gun with a fiery vengeance. As for Duggins, she's learned how to get into Garner's headspace when she needs to double for her.

"I just become her at times," said Duggins, who added that Garner really sets the bar high when it comes to being a warrior. "Come on! Just look at the action and how badass she is!"

The pair also gave Frazier a bit of a demonstration in stage fighting, with Duggins and Garner both showing off their moves. 

While Duggins has been in the screen fighting game for years, she had nothing but praise for Garner's skills and determination. "It's her the whole movie," she said. "You see it on her face the whole time."

"But she would come in and fix me and I would do it again and then I would look closer to what she did," Garner said, referring to the movie's brutal combat scenes. "But I'll never be like her… She just always takes anything and it's just elevated when she does it."

In Peppermint, Garner plays a woman whose husband and daughter are murdered in a drive-by. When she awakes from her coma, she dedicates her life to learning how to fight and kill, then seeks out those who took everything from her.

"This is hard R action. This is not a family movie or Miracles From Heaven," Garner told Frazier, referring to her 2016 religion-themed drama.

While Garner has mostly appeared in grounded dramas and family comedies in recent years, she's certainly no stranger to action -- including her turn as Elektra in 2003's Daredevil and 2005's Elektra, and her five-season run on J.J. Abrams' ABC spy thriller Alias, which came to an end in 2006.

ET previously caught up with Garner at CinemaCon in Las Vegas back in April, where she said it "felt great" to be a part of a movie that included a stunt team again.

"My stunt double and I have worked together since I think the third or fourth episode of Alias… So she's like my sister," Garner said of her reunion with Duggins. "So [it's been great] for the two of us to get to be together every day, to train together, to go back to all of that."

For more on Garner’s intense training and a look at some impressive fight moves with her stunt double, check out their full interview on Entertainment Tonight on Monday, Aug. 20. Check here for local listings.

Fans can see just how action-packed and dark Garner's revenge journey gets when Peppermint hits theaters Sep. 7.