Billie Eilish says it was "fun" stepping out of her "comfort zone" on her latest single, 'NDA'.

The Grammy-winner released the track from her eagerly-awaited second studio album 'Happier Than Ever' this week, and she has admitted the aim was to create something "unexpected" for fans.

Speaking to Zane Lowe on Apple Music 1, she said: “I really wanted it to be unexpected, almost. Honestly, it’s so funny, because I write with structure in my head about verses and pre-choruses, and then chorus, and then verse, pre-chorus, chorus, bridge, chorus, end."

The 19-year-old star also explained that conversations in therapy have inspired her lyrics.

She added: "It makes me talk through things, and then I think about them constantly. I talk through things in therapy that I don't even think about in my life.

"And then over the week I'm like thinking about, 'Wow, that thing we talked about in therapy, I should write about that. That's really interesting.'

"And it's really helpful, it brings it out of you and it's really necessary."

Billie went through a lot of "self-reflection" on the new album.

She added: "There was so much self-reflection that I was doing.

"I was realising things about my life that I had never even processed, and realised that I had never processed.

"And the same with things that I witnessed around me and saw happen. And just talking through it and getting it out of me, and then you know, making it sound good."

'Happier Than Ever', which is released on July 30, also features the previously released singles 'Your Power', 'my future' and 'Lost Cause'.