Sophie Turner returns to the small screen with a sparkle in “Joan,” a new drama about a jewellery thief so prolific she became known as “the Godmother” in Britain’s criminal underworld. But despite her aptitude for pilfering wigs, diamonds and fake accents, “Joan” is as much a story about the lengths a mother will go to for her child (played by Mia Millichamp-Long) as it is a heist caper.

It was that maternal love that Turner, who has two young daughters of her own, most strongly identified with when she was first approached about the project. Ahead of the series dropping in the U.K. (on ITV from Sept. 30) and the U.S. (on The CW from Oct. 2 and BritBox on Dec. 5), she sat down to talk with Variety about the most challenging aspect of filming “Joan,” meeting the real diamond thief who inspired the series and whether she’d ever return to the “ Game of Thrones ” universe.

How did you come to the project?

I auditioned for it — because she is so unlike any character I’ve ever portrayed. It came through my agent, and I did one audition while I was quite pregnant with my second child, and then a second audition a few days after giving birth. But it was actually a perfect time to audition, considering the themes of “Joan” and the challenges she faces. I had that fierce maternal instinct within me, which I believe enhanced my performance during the audition.

You’ve met the real Joan – what’s she like?

That was probably about a week before filming commenced. She was truly exceptional and a force of nature. She brought an incredible energy to the room. I enjoyed meeting her very much.

How does she reflect on her experiences?

When we met, we didn’t really discuss her life. By the time I’d met her, I’d already had the character in my mind and so my meeting her was purely out of curiosity. And now we talk about the most ordinary things. She enjoys interior design, and so that’s what we usually chat about, and obviously, fashion and similar topics. So we kind of discuss the things that Joan would be interested in. I think she needs to relive so much of her past by watching this show and doing these interviews and being a part of it, so I kind of want to give her that sweet relief of just talking about the jewellery she’s wearing. [Laughing] Like: “Where’d you get that from?”

What was the most challenging part of filming the show?

Probably the scenes with [Joan’s daughter] Kelly. The emotional core of the show is the relationship between Joan and Kelly, and every scene is simply heartbreaking. I developed a very close bond with Mia, who plays Kelly, and she is an incredible actress. It made everything ten times more challenging to act through. I mean harder in terms of emotional difficulty, but actually easier, because of how talented she is as an actress.

You were also going through a difficult period personally, including a divorce, around the time you filmed “Joan.” Did that feed into the role at all or did you manage to shut it out?

“Joan” was nearing its end around that time, and I had already completed all of my scenes with Mia. But, I was a new mother to my second child when filming began, so I already had that protective, fighting-for-my-kids spirit within me. And yes, it did feel like a fitting time to be involved with this subject matter. It was still forefront in my mind. I mean, you would do anything for your children, you would sacrifice everything for them, and so I completely understood Joan – I truly understood.

The show also explores that balance of being a mother and continuing to be a woman in your own right with your own identity. Did that resonate?

It was fascinating because there was talk of “maybe she’s just excellent at compartmentalizing.” Maybe that’s her way. And then the more I thought about it and the longer I had been a mother, from the time I got the job to the time I started, it’s kind of this… — I find that allowing yourself to be a 20-something year old, and to meet people, go out, work is so important in general for the child. So it’s all for the wellbeing of this person. I’m so glad that they’re gonna grow up and go: “Oh look, Mommy’s gonna go out and do this” and it’s so that she can come home and we can spend more time together at the end of the day… I think it’s important for them to see that I’m going out and seeing friends and not isolating. I used to be a big isolator. I had mental health struggles, and now I know the importance of them seeing me curate friendships, because they learn all their attachment styles from you. And so, of course, Joan’s work isn’t necessarily the best form of work, but it all boils back down to Kelly.

Absolutely. And on a lighter note, the Eighties fashion in the show is epic. How involved were you in styling Joan?

I did not know any better than our costume designer, Richard Cook. He was pulling in, like, vintage Mugler from the ‘80s, and making outfits from scratch with his hands. Those guys lived in the ‘80s so I trusted them. I wasn't alive around then. But I mean, we, all of us, became so immersed in this Eighties world and the music we were playing was ‘80s when we were getting ready and in the fittings, everything became Eighties-fied.

What was the most fun disguise you got to wear?

I played a Scottish woman, and she was such a delight because she was so sweet and innocent. All the characters Joan was portraying were very affluent or belonged to the upper class, and this one was a little more gentle and naive and needed some assistance. It was a fun role to play — and I enjoyed doing a Scottish accent.

You do a lot of accents in the show! Did you work with a dialect coach?

I did. I was granted some mercy through the fact that Joan is not an expert at doing accents and I thought, thank God for that. She’s not an actress. But she grew up admiring this life from afar, seeing adverts on her little old TV when she was young and so I think she does these “Dallas”-style, exaggerated versions of ‘80s glamor, and that was really fun to do.

Before we wrap up, I have to ask about “Game of Thrones.” Could we ever see the return of Sansa Stark?

Maybe. I mean, it would have to be the exact same cast and the exact same crew otherwise I wouldn’t go back and that would just be Season 9, and I don’t think we’re going to do a Season 9, but, I mean, I loved playing Sansa, and I do wonder often what she would be doing now. Where would she be five years later, what would she be doing? Would she still be queen in the North? Would she be a capable ruler? Would there be some other kind of terrible war that’s happened? I’d love to see it.

You’ve also played the iconic X-Men character Jean Grey. Was there any talk of you making a cameo in “Deadpool & Wolverine”?

No, I think there's, like, some sort of ending where they used a clip from “X Men.” I remember signing a contract. But no, that part of my life is over. I mean, maybe not — I love doing superhero action stuff, but I think the Jean Grey arc for me is probably done. It's had its run.

What’s next for you?

I just finished a TV show, and now I have a new project in the works with Kit Harington called “The Dreadful.” It's a horror film in the vein of Robert Eggers, set during the War of the Roses.

Do you feel like you’ve had time away and now you’re in a moment where you’re leaning into your career more?

I definitely had a quieter period. I focused on building a family and wanted to spend as much time with them as possible. Now I want them to see me working. Also, personally, I want to be back on my feet and doing what I love, because acting truly fulfills me. When I'm on set, I'm so happy. I'm so fortunate that I get to balance the two things that fulfill me most, being a mother and acting.

This interview has been edited and condensed for space and clarity.