The 20-year-old actress and the former Jonas Brothers musician first made their relationship known when they spent Thanksgiving together in November, and have now made things official on the picture sharing website after the fiery haired beauty posted a picture of Joe on her account this week.
The picture shows the 27-year-old singer smoking whilst on a boat and was simply captioned: ''Miami Daze (sic)''
The news comes after the DNCE frontman was said to be falling head over heels for 'Game of Thrones' star because she ''has her own money'' and isn't using him to get free dates.
A source said: ''[Joe is] smitten [because Sophie] has her own money. He loves her because she won't let him pay for her all the time, which is so rare in girls he meets. She insists on paying her own way for flights when he asks her to come see him and offers to pay. Plus, he thinks she's so smart and sexy.''
And despite having only been together for a short period of time, the 'Cake by the Ocean' hitmaker already believes the beauty is something special.
The source added: ''He's telling friends there's something different with her, and he knew it as soon as they met.''
Sophie and Joe were first romantically linked in early November when they were spotted cuddling up at the MTV Europe Music Awards.
A source said at the time: ''Sophie and Joe met through mutual friends. They have been dating for a couple of months. They spent Thanksgiving together in Mammoth Lake. They are really into each other and having a great time.''
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