Fifty Shades Darker: Taylor Swift and Zayn Malik release surprise song for upcoming film soundtrack

iTunes describes it as 'two of pop's brightest stars [teaming up] for a passionate duet'

Taylor Swift and Zayn Malik have released a surprise duet that will feature on the Fifty Shades Darker soundtrack.

'I Don't Wanna Live Forever' appeared in the US iTunes Store just before midnight in the US, eastern time.

iTunes describes it as "two of pop's brightest stars [teaming up] for a passionate duet." It was No. 1 on the US iTunes chart within an hour of its release.

Swift posted a teaser of the song with footage from the film on her Facebook page with a hashtag of the film title, which has received over 1.8 million views in three hours.

The song was recorded "in a week" at musician Jack Antonoff's house.

He tweeted that it "came together very quickly", and that it was written with Swift and American hip hop artist Sam Dew at his home.

Malik posted an image of the pair posing together on Instagram with one of Swift's cats.

The 'Bad Blood' singer and Malik, a former member of boyband One Direction and now-solo artist, swap verses during the song, with Malik singing in his typical falsetto.

He sings: "I don't want to live forever, 'cause I don't want to be living in pain/I don't want to fit wherever, I just want to keep calling your name/'Til you come back home."

This is the first song to be released from the soundtrack from the upcoming sequel to Fifty Shades of Grey that stars Jamie Dornan and Dakota Johnson.

It is also the first new music to be released by Swift in 2016, although that appeared to have little effect on her being named the highest-paid musician of the year.

Fifty Shades Darker is set for release early next year