This track was released on Avicii's album True last year in September, and the track is actually called 'Dear Boy'.
Here's the studio version just in case you haven't heard it yet:
I was pleasantly surprised when Avicii's manager confirmed that MØ was the singer on twitter last year, especially as I never thought that she would collaborate with a electronic house producer. The track is killer though and the tune is really catchy.
EDIT: Avicii released a remixed version of track a couple of weeks ago titled Dear Boy (Avicii by Avicii) with the un-altered vocals, and if you slow the song down you can really hear Karen's beautiful voice.. I never understood why he added vocal layers over her voice on the original version.
