Speaking to The Guardian, Tedder - who also penned ‘XO’ for the star as well as Ella Henderson’s newly-released debut ‘Ghost' - explained where he thinks that came from.

"I can’t speak for all of the songs that she does but I’ll say this: she does stuff on any given song that, when you go from the demo to the final version, takes it to another level that you never would have thought of as the writer," he said.

"For instance, on ‘Halo’, that bridge on her version is completely different to my original one. Basically, she came in, ditched that, edited it, did her vocal thing on it and now it’s become one of my favourite parts of the song. The whole melody, she wrote it spontaneously in the studio.”