The 22-year-old actress - who is best-known for her role as Sansa Stark in 'Game of Thrones' - has admitted to embarrassing herself in front of her celebrity crush after they were introduced by her fiancé Joe Jonas.
Recalling her first encounter with Justin at a friend's house in Miami, Sophie shared: ''I go upstairs and he's sat there shirtless in this dark room getting a head massage. And I was like, 'Oh my god! This is amazing!'
''So I was like, 'Hi, nice to meet you, Sophie,' played it cool, ran into the closet and like cried for five minutes.''
However, the awkwardness didn't stop there for Sophie, who performed a strange hand gesture when she was properly introduced to Justin.
Sophie - whose moved involved provocatively waving her tongue - told 'The Late Late Show with James Corden': ''Justin goes to Joe, 'Yo, Joe, I heard you got a new girl.' And Joe was like, 'Yeah, yeah, yeah, there she is, she's over there.'
''And I don't know what came over me to do this, but I turned around and I was like, 'Hi...'''
Sophie admitted that Joe, 29, has not let her ''live it down'' ever since.
But the actress is philosophical about the incident, saying Justin is probably used to fans doing strange things in his presence.
She said: ''That can't be the strangest thing that someone's done to him.''
Meanwhile, Sophie recently admitted she is ''excited'' to become Priyanka Chopra's sister-in-law.
Priyanka and Joe's brother Nick Jonas confirmed their engagement in India in August, and Sophie couldn't be happier to welcome the fellow actress into their growing family.
She wrote in an Instagram post: ''Wow. First I'm blessed with an incredible future brother-in-law, and now such an beautiful, inside and out, future sister-in-law. I'm so excited to welcome you into the family @priyankachopra . I love you both @nickjonas (sic)''
Listen to her new song 'I'll See This As A Blessing'.
This article is dedicated to Caroline Flack.
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