Jack Antonoff Shares New Details About Taylor Swift’s Most Emotional Song

Last night, we were treated to a rare television performance by Taylor Swift on The Tonight Show With Jimmy Fallon. It was Fallon's first show since returning from a bereavement leave — his mother recently passed away, and he left the show to attend to his family's needs.

Swift dropped by for a surprise set. In a performance with a piano, a guitar, and a few backup singers, she sang the ballad "New Year's Day" from reputation. Her voice was confident and smooth, and co-writer Jack Antonoff (and Lena Dunham's main squeeze) took to Twitter to share his thoughts on her show.

"[T]aylor doing new year’s day on fallon was beautiful," Antonoff wrote. "that song means a lot to me. happened so quickly at my apartment. we texted the next morning to make sure it wasn’t a dream."

We can only imagine being a fly on the wall during their writing session — Swift on her guitar, strumming out the chords she'd written, with Antonoff plugging everything into his computers and synthesizers (he appears to be a fan of Moog) in order to craft the perfect arrangements for the song. It may be a simple piano-based ballad, but it certainly took a lot of work to mix the instruments and her voice just right.

"New Year's Day" is about leaving behind the New Year's Eve party of the night and waking up to a new morning: still being weighed down by the expectations of a new year, but feeling excited and hopeful and ready to grow up. We couldn't imagine a more fitting tribute to Fallon's mom.