Sophie Turner has a "perpetual back problem".

The 29-year-old actress - who has daughters Willa, five, and Delphine, three, with her former husband Joe Jonas - discovered a recurring health issue while undergoing gruelling training for her role as adventurer Lara Croft in the upcoming Tomb Raider TV series.

Speaking on The Julia Cunningham Show, she said: "We've been doing eight hours a day, five days a week since February of last year, of training. Yeah, so it's been a lot.

"I've learned I have a perpetual back problem, but I also realized that it's much easier to kind of build muscle if you've ever worked out before in your life, which I never had, so it has taken me months and months and months to get into good shape. That's what I've learned."

Sophie is best known for her role as Sansa Stark in Game of Thrones but she insisted her years on the fantasy drama series didn't help prepare her for Tomb Raider because she was never involved in any action scenes.

Asked if Game of Thrones had helped her at all, she replied: "No, I was the cool queen who, like, didn't have to do that. I also just kind of was the one that got beat up, not the one doing the beating. So, it's quite nice to learn how to throw a punch and not just take it."

Meanwhile, Sophie recently admitted she would be open to the idea of playing Sansa again in the future, though she worries it could be a mistake after her alter ego got a "good" ending on Game of Thrones.

When asked about a possible return to Game of Thrones, she told Thedirect.com: "Show me the money. I don't know, I think it would be hard but also amazing to come back to it.

"But I feel that I was very happy with the way Sansa ended her story in Game of Thrones, and no one else was really happy with their ending. I feel like I got a good one, and so I don't know if I could revisit it."

She added: "Maybe it would be an utter joy, or maybe it would be trying to cling on to something that was magic back in the day that can't be recreated. I would have to see a script."