Taylor Swift’s friend Jack Antonoff shades singer's ex Joe Alwyn

Jack Antonoff laughed out loud when a fan asked him to sign a poster mentioning William Bowery, the pseudonym for pal Taylor Swift’s ex-boyfriend Joe Alwyn.

The Bleachers lead vocalist was stopped by a fan after a show on Friday. As a Reddit post shows, a fan held up a poster that said, “Who’s William Bowery anyway?”

The next day, during a signing event at Rough Trade Berlin, another fan approached Swift’s songwriting partner, with a similar William Bowery poster.

Antonoff had no other response other than shrugging and laughing it off.

For the unversed, Alwyn used the name William Bowery for his songwriting collaborations with now-ex on her albums Folklore, Evermore and Midnights.

Swift kept the identity of William Bowery a mystery until her Folklore: The Long Pond Studio Sessions documentary where she detailed the story behind the name.

“I came in and I was like, ‘Hey, this could be really weird, and we could hate this, [but] because we’re in quarantine and there’s nothing else going on, could we just try to see what it’s like if we write this song together?’”

The Anti-Hero hit maker added, that he “was just singing it, the way that the whole first verse [of Exile] is … I was entranced and asked if we could keep writing that one.”

Alwyn’s collaboration with then-girlfriend earned him a Grammy in 2021 when she won Album of the Year award for Folklore.

The Grammy-winning pop star, who has now moved on with NFL star Travis Kelce, made a special mention for Alwyn in her acceptance speech, “Joe is the first person that I play every single song that I write, and I had the best time writing songs with you in quarantine.”

However, the couple's Love Story came to an end in in 2023 after six years together.