Melanie C, Emma Bunton release duet video - watch
The Spice Girls bandmates covered the Elaine Paige and Barbara Dickson duet for Mel C's latest album Stages.
The track will be released on November 11 as a two-track CD and digital bundle.
Melanie C revealed on Twitter that she was wearing one of fellow Spice Girl Victoria Beckham's designs when she filmed the clip for 'I Know Him So Well'.
Discussing the duet with Digital Spy, she said: "I wasn't sure she would do it but when I asked her she squealed!
"It was so emotional when we first heard our voices together again. It's so Spice Girls. I'm so excited for people to hear it."