After tweeting about being obsessed with Sheeran's music, Swift later decided to take the British singer-songwriter on the road with her for her Red Tour. But before she asked him out on the road, the two met up for a songwriting session at Swift's Nashville home. It all came together shortly after Sheeran learned that Swift had written lyrics from his song "Lego House" on her arm during her Speak Now Tour.

"Two days later, I got an email saying she had been a fan for awhile and 'Should we write a song?'" Sheeran told Rolling Stone last year of their friendship. "So we hooked up and wrote two tunes, actually, one on the record and another that's still out in the ether somewhere."

The music video to one of those songs, "Everything Has Changed," was just released this wee (June 5). Apparently they wrote the song, which they've been performing together throughout her Red Tour, on a trampoline at her home.