Fifth Harmony Dishes on Taylor Swift & Calvin Harris: 'He's the Luckiest Guy in the World'

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Fifth Harmony's Camila Cabello is now a definitive member of Taylor Swift's girl squad, but she was once just a Swiftie like the rest of us. When the girl group joined T. Swift for a stop on her 1989 World Tour earlier this month, performing their hit single "Worth It," Cabello let her inner fangirl out.

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"Before we met and became friends, before our heart to hearts about boys and love and heartache and Internet slang, I knew every word of every song and said in every interview how much I looked up to her as an artist and as a person- and last night she invited us to perform on the 1989 tour and she was the sixth harmony!!!!!!!!!!!!!!!" the 18-year-old singer wrote on an Instagram of the epic performance. "I almost went into a fit of tears as we were going up the risers but I was like CAMILA PULL IT TOGETHER. LOL. Thank you so much Tay and her swifties for making us feel so welcome."

WATCH: Fifth Harmony Cleans Up at Teen Choice Awards in Style

ET's Katie Krause sat down with the Fifth Harmony girls to talk more about Taylor and what the “Bad Blood” singer has taught them about love and heartbreak.

“I went through a really bad breakup and she would literally stay up talking on the phone with me and giving me advice about how to get over it and deal with it,” Cabello said. “She basically just said talking is the best way to get through it. If you don't process those kind of emotions they kind of come back and bite you. She was somebody that was really there for me, to hear me vent, and that was really, really important.”

WATCH: Meet The Girls of Fifth Harmony

Not only does T. Swift write songs about love, the singer is living her own real-life love story right now with her boyfriend, Calvin Harris. Fifth Harmony dished about meeting the Scottish DJ at this year’s Billboard Music Awards.

"He was there, and we were invited to her after party," Dinah Jane, 18, told ET. "Him and his boys approached us-- they were like ‘Hey, what's up? What are you guys doing? Are you guys okay?’ But it was really, really sweet. He's a sweet guy. He's a lucky guy."

"He's like the luckiest guy in the world to be with somebody like her," Cabello gushed.

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