The 29-year-old singer found fame with her song 'Call Me Maybe' which became a huge hit after the 21-year-old popstar tweeted about it and both Justin and his former girlfriend Selena Gomez appeared in the music video.
Carly told Huff Post Live: ''If I had known he was going to tweet about it, I would have been hiding under a rock. It was life-changing. It all of a sudden got all of this attention.
''I'm so grateful to him and to Selena and everybody for that. It's one of those things you don't really know how to ever pay back.''
And Carly also revealed she is a huge fan of Justin's new music, including comeback singles 'What Do You Mean', and 'Where Are You Now'.
She said: ''I love his music, it's probably the best stuff I've heard from him so far. As a young musician you're constantly changing and I love what he is doing.''
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