"I Know Him So Well" is a song from the concept album and subsequent musical Chess by Tim Rice, Benny Andersson and Björn Ulvaeus. In this duet, two women – Svetlana, the Russian chess champion's estranged wife, and Florence, his mistress – express their bittersweet feelings for him and at seeing their relationships fall apart.
The duet was number one in the UK Singles Chart for four weeks in 1985, when released as a single by Elaine Paige (as Florence) and Barbara Dickson (as Svetlana), who laid down their vocals separately and never met during the recording of the song, only for the video and subsequent performances on Top of the Pops and the European tours. This recording remains in the Guinness Book of Records as the biggest selling UK Chart single ever by a female duo. Paige also appeared in the original London West End stage production of Chess.
In the United Kingdom on 18 September 2004, the BBC's All-Time Greatest Love Songs (hosted by Lionel Richie) saw the duet performed live by Paige and Dickson, together for the first time in 20 years, to a rapturous reception. Paige played her solo demo recording of the song on her BBC Radio 2 show, Elaine Paige on Sunday.
In January 2011 the Official Charts Company released a list of the top 10 All Time Best Selling Duets in which "I Know Him So Well" was placed seventh in the chart.
In 1987, a studio version of "I Know Him So Well" was recorded as a duet by Whitney Houston and her mother Cissy Houston for Whitney's sophomore album, Whitney. It was released as a final and 6th single from Whitney on November 30, 1988 in Australia, Germany, Netherlands, and Spain. There was no official music video produced for the Houston duet of song, however there are live performance video-recordings. The song version was included in the Whitney Houston North American leg of the Moment of Truth World Tour. The single was not promoted as heavily as previous singles from Whitney.
Robert Hilburn of La Times praised the duet thus: "The album ends on a graceful, intimate note as Houston is joined by her mother, singer Cissy Houston, on "I Know Him So Well," a ballad from the musical "Chess." Rolling Stone's Vince Alleti criticized the song and production: "Walden covers all these bases, out-schlocking Masser with "I Know Him So Well" — a genuine if frankly derivative show tune (from Tim Rice's Chess) treated here with deadly reverence..." St. Petersburg Times called duet lifting and praised the mother's role: "Mom adds a brief, welcome moment of grainy soulfulness to the album."
This single peaked at number 46 in Germany and in the Netherlands it peaked at number 14. The single did not appear in the Bubbling Under Hot 100 chart, unlike the 4 previous singles which all reached the Top 10.
"I Know Him So Well" was also covered by English recording artist Melanie C. The song was the first single to be taken from Melanie C's musical theatre-inspired and sixth studio album Stages. The song is a duet with Chisholm's fellow Spice Girls group member Emma Bunton. The song was released as a single on 11 November 2012. The b-side of the single is a cover of "You'll Never Walk Alone" from the musical Carousel. The music video for the song premiered on YouTube on 12 November 2012.