Jack Antonoff has Swifties spiraling after sharing a previously unseen photo of Taylor Swift in the studio last year. Antonoff, 40, included the pic in a slideshow of behind-the-scenes moments from New York City's Electric Lady Studios. "My room upstairs at ELS," he wrote via Instagram on Wednesday, September 18. "Everything is possible in here and i miss it when im gone. spend my days and nights in this small room dreaming about how this music will hit the stage - spend my time on stage honoring what's happened there while saving a piece of the show to bring back with me into this room." The first pic in the carousel showed Antonoff standing with a guitar and other gear. Other images featured some of the Bleachers frontman's collaborators, including Sabrina Carpenter, who worked with Antonoff on her latest album, Short n' Sweet. What really grabbed fans' attention, however, was a black-and-white photo of Swift, 34, and producer Sounwave dated December 21, 2023. Social media sleuths were quick to point out that Sounwave — who frequently works with Kendrick Lamar — is credited as a producer on several songs from Swift's 2022 album, Midnights, but is not listed anywhere on her most recent record, The Tortured Poets Department. Taylor Swift and Jack Antonoff’s Complete Friendship Timeline Swift dropped TTPD in April, two months after she announced her 11th album on stage at the 2024 Grammy Awards. At the time, she hinted that she'd been keeping the project under wraps "for the past two years." While Antonoff's new pic of Swift fits within the timeline of when TTPD was recorded, some fans are convinced a different project was in the works. In December 2023, Swift was spotted leaving Electric Lady Studios after a late-night recording session in a black shearling-lined jacket paired with a miniskirt and tights. She wore her hair down with her bangs swept to the side — the same way it’s styled in Antonoff's new pic. Lamar, 37, and Antonoff were reportedly seen leaving the studio shortly before Swift at the time. Jack Antonoff and Taylor Swift Antonoff has been known to fuel the Swiftie rumor mill in the past — and this instance is no different. "Taylor was totally up to something hiding in that corner jack," one fan wrote in the comments section, while another asked, "Hey so without being cryptic what exactly are u plotting..." A third user went the all-caps route, writing, "JACK WHAT ARE YOU TELLING US IN THE 7TH SLIDE????? TS12?? REPTV HELLO??????????????" Sabrina Carpenter Is the Latest Pop Star to Work With Jack Antonoff: See His High-Profile Collabs Swift's working relationship with Antonoff began in 2013 when they cowrote and produced "Sweeter Than Fiction" for the movie One Chance. They later collaborated on Swift's album 1989, which won Album of the Year and Best Pop Vocal Album at the 2016 Grammy Awards. Swift continued to team up with Antonoff on subsequent albums Reputation, Lover, Folklore, Evermore, Midnights and TTPD, even tapping Antonoff to produce several "From the Vault" tracks on her rerecorded albums. Antonoff previously stirred the pot when he revealed insights into the recording of Swift's breakup ballad "You're Losing Me," which was released following her split from Joe Alwyn last year. While celebrating its streaming debut via social media in November 2023, Antonoff noted that the song was "written and recorded at home on 12/5/21" — more than one year before the former couple's breakup made headlines.