Taylor Swift fans suspect her brother is singing on mysterious new track

On Sunday, Taylor Swift tweeted her support of a chilling "Look What You Made Me Do" cover performed by an artist no one's heard of.

The haunting track, which features prominent male vocals, premiered as part of the latest Killing Eve episode. That a Swift song would appear on a Phoebe Waller-Bridge show isn't surprising (the two have shared plenty of mutual admiration), but that it would be credited to "Jack Leopards and The Dolphin Club" is more of a head scratcher.

Per music streaming services, the Killing Eve cover is the only song under the band's name. When fans started looking into the band's history and the song's credits, a theory soon emerged that Swift had employed the help of her brother Austin Swift to create the cover.

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The song's production is attributed to Jack Antonoff (original producer on Reputation and co-writer of "Look What You Made Me Do") and the illustrious Nils Sjöberg — Swift's songwriting pseudonym first used on Calvin Harris and Rihanna’s "This Is What You Came For" in 2016.

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Additional sleuthing revealed that Swift's brother had previously used "The Dolphin Club" as his display name on Twitter — and that the band's cover art looked remarkably similar to a childhood photo of Austin Swift. Plus, the Daily Mail reported in February that Swift had explicitly asked Waller-Bridge to include her brother on the Season 3 soundtrack (though Daily Mail reports should always be greeted with a healthy dose of skepticism).

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As for the Jack Leopards bit, some Swifties say it's a two-part nod to Antonoff and Swift's iconic leopard look in the "Look What You Made Me Do" music video, if not her ability to rock leopard print writ large. (Mashable has reached out to Swift's representation regarding the identity of Jack Leopards and The Dolphin Club, but did not immediately hear back.)

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Fans are speculating Swift's motivations to use a pseudonym include, at least in part, her ongoing and highly-publicized dispute with music executive Scooter Braun, who acquired the master recordings of Swift's first six albums in 2019 against Swift's protests.