The British actress rose to fame as a teenager, portraying Sansa Stark on the hit fantasy series, and she admits growing up in the limelight was tough as she struggled to deal with negative comments about her changing looks on social media.
"I went through a bit of a dark place, I was not happy with myself," the now-20-year-old tells Net-A-Porter's EDIT magazine. "I think for me, and for every young girl out there, body image is such a big thing, especially if you are in the public eye. People comment on (your appearance) and... Ugh."
However, Sophie subsequently discovered working out did wonders for her confidence after hitting the gym to train for her new role as mutant superhero Jean Grey in the forthcoming X-Men: Apocalypse. The actress was put through her paces by a professional trainer, assigned to her specifically for the film.
"When I was forced to get into shape and eat healthily, my skin cleared up and I felt energetic all the time," she smiled. "It totally changed me."