Songwriter Julia Michaels has opened up about the creative process behind Selena Gomez's single 'Good For You', which she wrote in less than an hour. 

She paid a visit to On Air With Ryan this week and spoke about penning the track, which was hugely successful for Gomez, and revealed that it flowed naturally from an idea she had made a note of on her iPhone:

"Sometimes I'll have like an idea, like a voice note. When we did 'Good For You,' we actually did it on a Sunday in like 45 minutes. We had like an hour left in the studio and I had '14 carat' written down in my notes on my phone, and I kind of just went in the room and sang pretty much from the first verse down to the end of the chorus; just straight on the mic."

Michaels, who also wrote Justin Bieber's 'Sorry' and Hailee Steinfeld's 'Love Myself', added: "I came out and my song husband Justin Tranter finished it with me. And I think we just pitched it to Interscope. We thought, 'What about this?' And in about three months, it was a single!"

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Watch the music video for 'Good For You' along with an interview with Michaels below: