All surprise performances on Taylor Swift's '1989' tour are free of charge!

Pop star Taylor Swift brought in The Band Perry to play at her '1989' tour and said all of her surprise guests come to perform for free.

The Band Perry played 'If I Die Young', the 2010 smash single from the band's self-titled album, at Swift's concert in Indianapolis, was reported.

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Before introducing the family band, the 25-year-old 'Blank Space' hitmaker addressed fans' questions about how she chooses special guests to join her on tour.

"I want to remind you that anyone you see on the 1989 world tour coming out to surprise an audience... They're doing it for free out of the goodness of their heart because they wanted to come and play for you and surprise you. Any guest artist that you see on the 1989 tour stage had the opportunity to surprise any crowd at any show and they chose you, Indy," she said.

Other guests on her 1989 tour have included actress Julia Roberts, who said she hopped on stage after meeting Swift at the meet-and-greet before the show, Wiz Khalifa, Rachel Platten, Avril Lavigne, Lisa Kudrow, Selena Gomez, Justin Timberlake, and countless performers.