The 63-year-old actress returned to the franchise for the first time since 1991's "Terminator 2: Judgment Day", and underwent intensive training to reprise her iconic role as Sarah Connor in the new movie.
She says that the training and strict diet left her so thin she needed her butt built back up to a normal size when she turned up to filming.
"There were no carbs in my life for a year. I got so lean, when I arrived they had to build me a butt," Linda tells British morning show host Lorraine Kelly. "They added bottom, something you don't ever see coming, who wants more bottom, but apparently... I shouldn't give my secrets away!"
Discussing how she prepared for the new movie, in which she stars alongside Arnold Schwarzenegger, Mackenzie Davis, Natalia Reyes, and Edward Furlong, Linda reveals: "Time off was military training, Spanish lessons, scuba, we had to do it all. There was never a moment we weren't learning something or acting."
In fact, the star found filming the movie so tough, she jokes that she might have to resort to extreme measures to duck out of franchise creator James Cameron's planned sequels.
"I've been threatening to fake my own death so I wouldn't have to do the next one if there is one. It really was hard, it was the hardest and the greatest I've ever done," she quips.
"Terminator: Dark Fate" debuts in cinemas on October 23.