The 21-year-old actress and her 20-year-old 'Game Of Thrones' co-star decided to get the date they secured their role as Sansa and Arya Stark in the popular fantasy series inked on them.
Speaking to Elle magazine about the inking, the 'X-Men: Apocalypse' star said: ''We do! We always said that we wanted them so we got the date 07.08.09 on our arms because that's the date that both of us found out we'd got our roles in 'Game Of Thrones'.''
And Sophie has revealed the pair went ahead with the body art when they both had a ''day off'' from filming in Belfast, Ireland.
She added: ''So when we had a day off from filming in Belfast we just went to a tattoo place and got it done.''
Sophie has admitted she would ''love'' to go under the needle and expand her tattoo collection, but her job in front of the camera makes it ''really difficult'' for her, and if she was to have another etching done she would have to be ''pretty selective'' about what it was and where it went.
She explained: ''You know, I would love more but it's really difficult to cover up tattoos for roles so I'd have to be pretty selective about what I got and where I got it! Angelina Jolie can kind of afford to do that - everyone wants her so they're willing to cover her tattoos up. I'm not quite there yet.''
But it is unknown whether Sophie will get a tattoo dedicated to her new fiance Joe Jonas.
Sophie announced her engagement on social media on October 15, where the couple posted matching pictures of their rings.
And the star was believed to be ''totally surprised'' when the 'cake By The Ocean' hitmaker popped the question.
Speaking previously, a source said: ''Sophie was totally surprised. Joe is a romantic. He is really so in love with Sophie and she's so in love with him.''
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