"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 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.

Before the release of the album, Allen posted the song, then titled "Who'd of Known", on her MySpace account, revealing that she sampled Take That's single "Shine" and wrote: "I ripped off the chorus from Take That and can't be bothered with the paperwork.", for which the single was almost not included on It's Not Me, It's You. The singer pointed out in an interview that "Greg [Kurstin] just played the chords and I sang and we were like, 'That's great, really hooky.' Then when we played it back to someone, they pointed it out that it was, essentially, 'Shine'", and, while the band did not agree to sing on it, they gave her permission to record it, as they liked the song. The group was also credited as co-writer.

Musically, "Who'd Have Known" is set in common time and has a metronome of 84 beats per minute. It is played in the key of F major and follows the chord progression F—Fmaj7/A—E♭—E♭5—Gm7—F, while the piano and guitar are used for the background music.

...
Wikipedia