The Blurred Lines star put on a show in Abu Dhabi on Saturday night (22Nov14), and apologised to the crowd for a slew of vocal problems which he blamed on a nasty cold.
Williams admitted he needed some help singing his popular track Happy, so he brought out former Spice Girls star to provide the vocals. Video footage shows Halliwell performing the song while Williams dances around.
The Brit later shared her big moment with fans by posting a link to the footage on her Twitter.com page, as well as a picture of herself posing with the Grammy Award winner.
Halliwell was in the country to support her fiance, Formula One team boss Christian Horner, at the Abu Dhabi Grand Prix.