The 28-year-old singer slow danced with the 'Candy' hitmaker as they belted out the lyrics to 'Dream A Little Dream', taken from Robbie's new album 'Swing Both Ways', at the Under 1 Roof charity concert, held at London's Eventim Hammersmith Apollo.
Lily kicked off the show with her 2008 hit 'The Fear', which saw Chris playing acoustic guitar, while showing off his cheerleading skills.
Her short five-song set was then closed with Tim joining her on the piano, while they sang her cover of the band's 'Somewhere Only We Know', from the John Lewis Christmas advert, which is currently positioned number one in the charts.
The event - hosted by Fearne Cotton - was organised by Coldplay to raise money for the Kids Company, which helps support vulnerable children and young adults in London and Bristol.
The novel's author saw a cut of the film and loved each of the changes the movie's director had made.