Liverpool, UK - Taylor Swift shocked fans by performing a track made famous by her ex, Calvin Harris, and fellow superstar Rihanna as her latest surprise song on The Eras Tour.

Just when you thought the 34-year-old pop star couldn't come up with any more twists, she now has fans mourning a surprise song they didn't even know they could lose!

During her second night in Liverpool on Friday, Taylor kicked off her acoustic set with a rendition of This Is What You Came For – a 2016 dance-pop hit famously sung by Rihanna.

Despite RiRi being the face of the track, the Karma singer was actually the one to write it!

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The drama dates back to the era in which Taylor and Calvin were still going strong, and Taylor opted to keep her involvement a secret at first.

When the track first dropped, Nils Sjöberg was credited as a songwriter alongside the 40-year-old DJ, but TMZ later broke the story that the former was actually Taylor behind a pseudonym.

But the cracks in Taylor and Calvin's relationship soon became evident when Calvin was asked about collaborating with his then-girlfriend shortly after the song came out.

"I can't see it happening," he said, unsurprisingly leading to some serious hurt on Taylor's end.

Calvin eventually confirmed that it was, in fact, Taylor who wrote the lyrics and provided background vocals, but he affirmed that he wrote the music and did the arrangement.

When the two split in June 2016, the bad blood was quickly evident, and the Scottish hitmaker lashed out at Taylor in a series of since-deleted tweets that accused her of making him "look bad" by fighting for recognition of her involvement.

Flashing back to today, Swifties are over the moon to see Taylor reclaim the song, and many are now convinced she will include a version of the song with her own vocals in the vault tracks of the ever-elusive Reputation (Taylor's Version).

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Somehow, This Is What You Came For wasn't even the most jarring moment of the night, as after that performance (which also featured snippets of gold rush from evermore!), she took to the piano to play a heartwrenching mashup of The Great War and You're Losing Me.

Taylor returns to Anfield Stadium for one more night in Liverpool on Saturday before heading to Cardiff on Tuesday.