The "Game of Thrones" star, 23, has been candid about the personal struggles she has faced since shooting to fame on the hit fantasy drama series, previously admitting she battled depression and even contemplated suicide as a teen facing scrutiny in the public eye.
Sophie has also credited Joe with helping to pull her through some hard times, but in a candid new interview, she reveals his approach to tough love at the start of their romance in 2016 actually led the young couple to part ways.
"I was going through this phase of being very mentally unwell (when we first met)," the Brit tells the U.K.'s Sunday Times. "He was like, 'I can't be with you until you love yourself, I can't see you love me more than you love yourself.' "
"That was something, him doing that. I think he kind of saved my life, in a way."
However, the break-up didn't last for very long. "It was the worst day of our lives," Sophie confesses. "For a second we both had cold feet, then 24 hours later we were both like, 'Never mind.' "
She and Joe, 29, soon became inseparable, and the actress recently heaped praise on the "Sucker" hitmaker for helping her recognise the need for self-love.
"I love myself now, or more than I used to," she told U.S. self-help guru Dr. Phil McGraw last month (April 2019) on his "Phil in the Blanks" podcast.
"I'm now with someone that makes me realise, you know, that I do have some redeeming qualities, I suppose, and when someone tells you they love you every day, it makes you realise why that is, and I think it makes you love yourself a bit more."
The stars have since become husband and wife after tying the knot in a surprise ceremony in Las Vegas on 1 May, shortly after attending the 2019 Billboard Music Awards together.
The couple, which became engaged in 2017, is now planning to celebrate its nuptials with a more formal ceremony for family and friends in France this summer.