Pop superstar Taylor Swift surprised fans Friday by releasing her first new music in two years -- an R&B-tinged duet with former One Direction member Zayn Malik.

The track, "I Don't Wanna Live Forever," will be the theme song for "Fifty Shades Darker," the sequel to "Fifty Shades of Grey" that will hit theaters in February.

The track, which immediately went to number one on the iTunes chart for most downloads, is Swift's first song since her chart-topping 2014 album "1989."

In contrast to the perky Nordic pop of "1989," the new song has a sensual R&B feel as Zayn, mostly in falsetto, and Swift alternate verses about romantic longing over a stripped-down beat.

The song is more in line with the recent style of Zayn, who has gone for a more sexualized image and R&B sound since leaving his squeaky clean British boy band last year. He has gone by just his first name as a solo artist.

Swift's collaboration with Zayn will be all the more intriguing to fans as she used to date his One Direction bandmate Harry Styles, who publicly fell out with Zayn.

Swift's "1989" was one of the top-selling albums in recent years and won the Grammy in February for Album of the Year.

But Swift, who turns 27 next week, has been uncharacteristically quiet in recent months other than appearing in the celebrity press over her break-up with DJ Calvin Harris and her feud with rapper Kanye West over an unflattering song.