Justin Bieber and Taylor Swift wrote a song together!

World, brace yourselves for the exploding heads of 13-year-old girls everywhere. Justin Bieber and Taylor Swift -- each with enough star power in their own right to draw the heart palpitations and collective drool of every preteen on the planet -- have collaborated on a song. In an interview yesterday, the Bieb revealed he and the country crooner worked together for a tune on his third album called Believe, due out this summer. It's like if "Twilight" and "Hunger Games" had a baby and named it Katy Perry, it would be this exciting.