Katy Perry performs this surprising song on Taylor Swift's Eras tour

There's no more "bad blood" between Taylor Swift and Katy Perry — in fact, they've bonded over it. Perry attended the first night of her Eras tour in Sydney on February 23, where Swift performed four shows in a row, and she sang along to a very surprising song.

After the show, Perry posted a slideshow of the night on Instagram, starting with a selfie of her and Swift backstage. "I saw an old friend shine tonight," she wrote in the post. She even tagged her spot as "Swifties" to prove her fan status.

She also included photos of herself receiving friendship bracelets from fans and singing "You Belong With Me" with Rita Ora in the VIP tent.

Even more surprising, Perry included a clip of Swift performing "Bad Blood" in her post. During the chorus, she turns the camera towards herself and gives a shocked expression before giving in and singing along.

Taylor Swift and Katy Perry backstage at Swift's Eras Tour Instagram/Katy Perry

"Bad Blood" was at the center of Swift and Perry's initial feud. In a 2014 interview with Rolling Stone , Swift revealed that the 1989 song was about a female artist who hired a backup dancer while on tour, but didn't reveal who. "She basically tried to sabotage the entire arena tour," she said. "She was trying to hire a bunch of people from under me."

Perry understood the quote was about her and reacted to Swift's comments on Twitter days later. "Beware Regina George in sheep's clothing..." she wrote. She went on to respond multiple times over the next few years, most notably with her 2017 song "Swish Swish."

However, the two began to patch things up after Perry offered Swift a real love offer in May 2018, with Swift expressing her gratitude on her Instagram Stories. The two made their new friendship official when she guest-starred in Swift's 2019 video for "You Need to Calm Down," where she dressed up as a hamburger with Swift Fries.

While the Eras Tour reunion marked Swift and Perry's first reunion since the video, the two have continued to support each other from afar, with Perry praising Swift's 2020 album Folklore .