"Everything Has Changed" by Taylor Swift
This one's kind of obvious but still merits mentioning! Taylor Swift told MTV News that she collaborated with Sheeran on the song. "Yes, I actually I wrote a song with Ed Sheeran on a trampoline in my backyard for the new album . . . we had been writing a song and I was like 'Hey, I just got a trampoline. You want to see it?' And so, he brought the guitar for some reason. We ended up writing an entire song out there."