Taylor Swift Sings Ex-Boyfriend Calvin Harris’ Song

Taylor Swift performed ex-boyfriend Calvin Harris' “This is What You Came For” song at her concert in Austin, Texas, on Saturday.

Swift surprised about 80,000 concertgoers when she performed the song at the Circuit of the Americas race track for the first time live. “I've never played this song live before," Swift told the crowd. "But if you know it, maybe you could sing along, and then I could get to know what that feels like to hear it sung back to me."

Taylor co-wrote the song with Harris under the pseudonym Nils Sjöberg. After Taylor's publicist revealed that she was the co-writer, Calvin took to Twitter to slam her publicly. “Hurtful to me at this point that her and her team would go so far out of their way to try and make ME look bad at this stage though,” read one of his July tweets.

Although it was the first time she performed the song live, it wasn't the first time Taylor made reference to the song. This summer, she posted a video on Instagram of her friend Gigi Hadid walking the runway for Tommy Hilfiger to the tune while Swift and model friend Martha Hunt mouthed the words.

The concert came just days prior to a very important milestone in Taylor's career. "It's been about 10 years since my first album came out when I was 16," she stated. "And since then, I felt like I've been opening up my journal and letting you read it. And it's so amazing to know that 10 years later, you still feel like reading it, and you still feel like coming out and being here tonight.”

Taylor then reflected on the year of her life in which she thinks she learned the most. “I would still say that it was when I was 15," she said as the perfect segue to her song, “Fifteen.”