The singer opened up about her experience writing songs for folklore and evermore with Alwyn, who is credited under the pseudonym William Bowery. Together, they co-authored "exile" and "betty" on folklore and "evermore," "champagne problems," and "coney island" on evermore. While Swift touched on their relationship on at least a song or two on both albums, the songs they co-authored weren't about their romance—unsurprisingly, given how private they are. Instead, Swift explained, she chose to write "sad songs" with him on purpose.

When it came to "exile," Swift recalled, "I do remember the exact moment that I walked in and he was playing that exact piano part. And all I had to do was follow the piano melody with the verse melody. So because the vocal melody is exactly the same, pretty much it's mirrored with the piano part that he wrote. And we did the same thing with 'Evermore,' where I'll just kind of hear what he's doing and it's exactly, it's all there. All I have to do is dream up some lyrics and come up with some gut-wrenching, heart-shattering story to write with him."

"Joe and I really love sad songs," she added. "We've always bonded over music. ...We write the saddest. We just really love sad songs. What can I say?"

Swift admitted that if they hadn't been quarantining together, their collaborating might have never happened. "He's always just playing instruments and he doesn't do it in a strategic 'I'm writing a song right now' thing," Swift said. "He's always done that. But do I think we would have taken the step of, 'Hey, let's see if there's a song in here. Let's write a song together'? If we hadn't been in lockdown, I don't think that would have happened, but I'm so glad that it did."

Working together with Alwyn, Swift told Lowe, "in a way, it wasn't [surprising] because we have always bonded over music and had the same musical tastes. And he's always the person who's showing me songs by artists and then they become my favorite songs or whatever."

You can watch Swift's full interview below: