Ed Sheeran is already pulling double duty as Taylor Swift's [article id="1073635"]tourmate[/article] and duet partner -- their [article id="1706558"]"Everything Has Changed"[/article] will serve as Swift's next single in the UK -- but it's looking like things might not stop there.

Because as Sheeran explained to MTV News, he and Swift have actually collaborated two more songs -- even recording one of them. So whatever happened to that unheard track? Well, right now, it's residing on Sheeran's phone."

"We did do a lot of stuff, but I don't know whose record it will end up on," Sheeran said. "We did three songs, and recorded two, and one went on her album, which is the next single. But we'll see what happens with the other one, there's no specific plan so far, it's just chilling on my iTunes right now. It's on my phone."

So who knows? Perhaps the song will end up on Sheeran's new album (though we're not sure how it will fit in amongst all the [article id="1706937"]"rap-metal"[/article]) Or maybe, he'll just scrap it in favor of another duet with Swift. After all, the two have established quite a bond, both in the studio, on the road, and at a Chinese restaurant near you.

"She's so down to earth, despite being one of the biggest acts of the planet, you don't really see that side of her unless she's on stage," Sheeran said. "When she's on stage, she's an entertainer and a performer, but when she's off stage, she spends half the time tossing cat treats to her cat. It's a very relaxed backstage area, and when we're not on tour, it's just, like we went out for a stir-fry the other day."