who sang someone that i used to know
Kimbra
Somebody That I Used to Know
The track was recorded between January and May 2011 with Gotye struggling to find a suitable female vocalist, as a "'high profile' female vocalist" cancelled the collaboration at the last minute, and Kimbra "lucked out as the replacement". 
wiki:951938
Somebody That I Used to Know [SEP] Composition and recording
It felt weak." The track was recorded between January and May 2011 with Gotye struggling to find a suitable female vocalist, as a "'high profile' female vocalist" cancelled the collaboration at the last minute, and Kimbra "lucked out as the replacement". He tested his girlfriend, Tash Parker, but "somehow their happiness meant that it didn't work out" so he followed the recommendation of the song's mixer and used Kimbra's vocals. Martin Davies from Click Music considered the song "instantly captivating", and named Kimbra's voice "clean and sugar-soaked", further commenting that it bears an "uncanny resemblance" to singer Katy Perry. Gotye stated that the song was "definitely drawn from various experiences I've had in relationships breaking up, and in the parts of the more reflective parts of the song, in the aftermath and the memory of those different relationships and what they were and how they broke up and what's going on in everyone's minds.