The two actresses star as on-screen sisters Sansa and Ayra Stark in the HBO fantasy drama series, and though the pair are close friends, they haven't shared screen time since season one, so when their characters came face-to-face again in this week's episode, the British stars couldn't concentrate.
Speaking to Entertainment Weekly, Sophie, 21, said: ''Our first scene together was our reunion scene and we f***ed up so many times.
''We couldn't keep a straight face! Our relationship is so close, but it's only that fun side, never the business side.
''I was nervous. It just terrified me. It's like performing for your mum. When somebody is watching you, you don't do it quite as well.
''But in the long run I think it benefits us because we can be free with each other in our acting. We're not afraid to go there with each other because we feel so comfortable around each other.''
Maisie, 20, who plays Ayra, agreed with Sophie as she found it hard getting into character with her close friend watching.
She said: ''It was the weirdest thing when we shot our first scene together.
''We were both embarrassed to do our thing in front of each other. It took a few hours for us to get serious and actually do it.
''Later it was fine on set and we could concentrate, but it was so hard to get into character with Sophie in front of me.''
Season seven has already had a heartwarming reunion after Bran Stark (played by Isaac Hempstead Wright) returned to their home of Winterfell and met his on-screen sister Sansa.
All three of the characters haven't shared screen time at the same since season one.
When reading the script, Sophie said: ''I was like in a corner scrolling on my phone and I was so overwhelmed by Bran and Sansa and Ayra meeting again.
''So I was sitting in the corner going 'Ahhh!' and everybody there were fans of the show and going 'What is it?' and I rang Maisie up and was like 'Can you believe it? It's amazing'.''
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