While some listeners might expect that Taylor and Joe (aka William Bowery) had worked on love songs together, the two collaborated on the "Folklore" songs "Exile" and "Betty."

"Exile" is about the end of a toxic romance, and "Betty" is about a love triangle between three teenagers (it also revealed the name of Blake Lively and Ryan Reynolds' third daughter).

In her documentary, Taylor explained that Joe actually wrote the piano portion of "Exile."

"Joe plays piano beautifully and he's always just playing and making things up and kind of creating things. And 'Exile' was crazy because Joe had written that entire piano part," she shared. 

When she heard her beau singing, she wanted to continue working on the song with him.

"He was singing the Bon Iver part, the 'I can see you standing honey, with his arms around your body, laughing but the joke's not funny at all. He was just singing it," she continued. "And I was entranced and asked if we could keep writing that one."

His contribution convinced her that it needed to be a duet. Bon Iver was later asked to sing the other part on the track. 

"It was pretty obvious that it should be a duet because he's got such a low voice and it sounded really good sung down there in that register," she said. "And then, we're really, really, really big Bon Iver fans."

She said that Aaron Dessner helped to get Bon Iver on the song. But, it was his work on "Betty" that convinced Taylor that they could co-write hits together.

"I just heard Joe singing the entire fully formed chorus of "Betty" from another room. And I was just like 'Hello,'" she explained in the doc. "It was a step that we would never have taken because why would we have ever written a song together?"

Taylor then decided to ask Joe if he wanted to work on music with her. 

"So this was the first time we had a conversation where I came in and I was like, 'Hey, this could be really weird, and we could hate this, so 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?" she added.

Thankfully for fans, Joe did say yes to working on "Folklore." Taylor's eighth studio album was nominated for several Grammy Awards, including Album of the Year and Best Pop Vocal Album.

The pop icon also received nods for "Cardigan" (Best Pop Solo Performance and Song of the Year), and "Exile" (Best Pop Duo/Group Performance).