This was Mutya Buena, Keisha Buchanan and Siobhan Donaghy's first public performance together in over a decade.
The band have reformed as Mutya Keisha Siobhan and covered Rihanna's hit single 'Diamonds'.
Performing at Ponystep's New Year party, the girl group also sang their first Sugababes single 'Overload' and hit single 'Freak Like Me'.
Buchanan tweeted pictures of the reunited trio, writing: "Argggh love my sisters."
Buena added about the gig: "We promised every1 something frm us by new yrs and we gave it hope u all enjoyed last nite who ever was there an enjoyin it on youtube xxxxx."
Donaghy wrote: "Happy new year everyone!!!! Well this certainly goes down as the best yet."
Mutya Keisha Siobhan hinted in November that their new album is better than their 2001 debut One Touch as the Sugababes.
Watch the video below of the trio at their surprise gig: