On "Folklore," he co-wrote “Exile” and “Betty," and on girlfriend Swift's follow-up album, "Evermore," he was credited with being one of the writers on “Coney Island,” “Champagne Problems,” and “Evermore.”
However, when the albums came out, Alwyn didn't use his real name in the credits, instead using the pseudonym William Bowery.
During an appearance on “The Kelly Clarkson Show," Alwyn explained why he decided to adopt the fake name.
"We chose to do it so that people, first and foremost, would listen to the music first before dissecting the fact that we did it together," Alwyn said.
Alwyn noted that he didn't choose the name William Bowery out of thin air: The pseudonym has a special meaning behind it.
"It was a combination of William, my great-grandfather, who I never actually met, (who) was a composer," Alwyn said. "He wrote a lot of classical music and he wrote a lot of film scores. And then Bowery is the area in New York that I spent a lot of time in when I first went over there. "
"I love that," Clarkson responded.
At one point, she joked that the name sounded "very fancy" and Alwyn laughed that William Bowery sounded like "a kind of Agatha Christie character who should be wearing a monocle with a big mustache."
Swift, 32, didn't reveal that Alwyn, 31, was actually the mystery writer until she talked about the album with some of its creators in her November 2020 documentary, "Folklore: the long pond studio sessions."
“There’s been a lot of discussion about William Bowery and his identity, because ... it’s not a real person,” she said at the time, per E! News.
“So, William Bowery is Joe," Swift added.
Alwyn also talked about his work in the album during a May interview with GQ and he recalled what it was like to create the melody and first verse of "Exile," which is one of the most popular tracks on "Folklore."
“It was really the most accidental thing to happen in lockdown," he said. "It wasn’t like, ‘It’s three o’clock, it’s time to write a song!’ It was just messing around on a piano and singing badly and being overheard and then thinking, you know, 'What if we tried to get to the end of it together?'”
Alwyn couldn't believe it when his notes wound up being produced by The National’s Aaron Dessner and Justin Vernon, the frontman of the indie folk band Bon Iver, agreed to be on the vocals.
“Sending it to Justin with the idea of doing a duet and getting voice notes back of him singing over the top and stuff was surreal," Alwyn said. "It was a perk of lockdown.”
Although he doesn't plan on writing any more music, he said it was "fun" to be William Bowery for a while and to make that music with Swift.
"I was proud of it. It was nice getting such a positive reception," he said.
Thanks to his work on "Folklore," Alwyn won a Grammy as a co-producer on the album, which won Album of the Year at the 2021 Grammys.