《Who'd Have Known》is the fifth and final international single (fourth and final in the United Kingdom by British recording artist Lily Allen from her second studio album, It's Not Me, It's You. Written by Allen and Greg Kurstin, while interpolating Take That's single "Shine", the song was released as the fifth and final single from the album, but fourth in the United Kingdom, on 30 November 2009 by Regal Recordings. Contemporary critics complimented the song and Allen's warm vocals, while the music video portrays her as a groupie of Elton John. 　　The song is prominently sampled in American rapper T-Pain's 2011 song "5 O'Clock", on which Allen is credited as a featured artist.