Jack Michael Antonoff is an American singer, musician, songwriter and record producer. Antonoff is the lead singer of indie pop band Bleachers, and a guitarist and drummer in the indie rock band Fun. He was previously the lead singer of the indie rock band Steel Train. Jack has worked with Taylor on producing many of her songs, multiple being from 1989.

You Are In Love was written about his relationship with Taylor's friend, Lena Dunham.

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