The 23-year-old actress stars as Sansa Stark in the HBO fantasy drama and went through her much of teenage years on the show, and has said that being a high profile star whilst going through puberty left her struggling with depression, as she was constantly worried about her image.
She said: "I think it only went down hill when I started to hit puberty, really puberty though at like 17 and my metabolism was slowing down massively, I was gaining weight and then there was the social media scrutiny. You see ten great comments and you ignore them. One negative comment and it just throws you off.
"People were like, 'Damn Sansa gained 10 pounds' or 'Sansa needs to loose 10 pounds', 'Sansa's got fat'. I would just say yeah, I am spotty, I am fat, I am a bad actress and I just believed it."
And the blonde beauty admits she had a "weird fascination" with suicide at the time, but doesn't believe she ever would have taken her own life.
She added: "It's weird I say I wasn't depressed when I was younger but I used to think about suicide a lot. I don't know why though maybe it was a weird fascination I used to have, yeah I used to think about it but I don't think I would have ever gone through with it."
Now, Sophie says she feels better about herself, and credits her fiancé Joe Jonas with giving her a newfound self love.
Speaking to Dr. Phil on his podcast 'Phil in the Blanks', she said: "I am with someone that makes me realise that I have some redeeming qualities and when someone tells you they love you everyday it really makes you think why that is, so I think that makes you love yourself a bit more."