EXCLUSIVE: 'Allegiant' Stars Shailene Woodley and Theo James Impressively Scale 80-Foot Wall

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Only ET was behind the scenes of The Divergent Series: Allegiant to get an exclusive look at how they pulled off their death-defying stunts.

Shailene Woodley and Theo James return for the third installment in the Divergent series, and they filled ET in on what it was like filming one of the movie's most intense stunts: tackling "The Wall."

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"We did this bit when Shai had to be facing down and I had to be the other way, and it was a little daunting," James said of scaling the 80-foot concrete structure.

"I was facing the ground, walking backwards," Woodley explained. "I was holding onto Theo's shoulder like it was the last thing!"

In the sci-fi adventure flick, Beatrice Prior (Woodley) and Tobias Eaton (James) get past the wall enclosing Chicago and venture into the world outside, which they quickly learn is more dangerous than ever before. The duo must determine who they can trust as a ruthless battle erupts in their new environment, which threatens all of humanity.

WATCH: Shailene & Theo Lock Lips in 'Divergent'

Fellow co-star Miles Teller told ET he's doing all of his own stunts in the movie and even went to the shooting range to prepare for filming. Meanwhile, Ansel Elgort revealed that his action scenes might be too much for his wardrobe to handle.

"My whole costume got torn up yesterday," Elgort said. "This is a new one. By the end of today it'll get totally torn up."

The Divergent Series: Allegiant hits theaters March 18.