Taylor Swift, "Everything Has Changed" (2012)
Though Taylor Swift has collaborated with top-shelf songwriters from Nashville pro Liz Rose to Swedish pop mastermind Max Martin, Sheeran is among the few who also sang a duet with her. The two wrote "Everything Has Changed" at Swift's home, where, according to Sheeran, he questioned a chord Swift wanted to use. She responded to his challenge playfully, pointing to her shelf full of Grammys, but he held his ground: "She didn't like that but I forced it upon her." The session was playful, with the two superstars completing the song while bouncing on Swift's newly purchased trampoline – because, as Swift told MTV, "The combined maturity of us is like eight years old."