Published Tuesday, 22 September 2009
Keisha, 24, is to launch a solo career following her exit last night from the group after 11 years.
She is being replaced by this year's Eurovision Song Contest entrant Jade Ewen who joins Heidi Range and Amelle Berrabah.
A statement on behalf of the group said: "The current line-up of the Sugababes has disbanded."
The band will press ahead with plans to release new album Sweet 7 on November 23.
Speaking about her departure on Tuesday, Keisha said: "I'm sad to say that I am no longer a part of the Sugababes.
"I've had a great time and have achieved more then I ever thought I would. Although it was not my choice to leave, it's time to enter a new chapter in my life."
The band has long been dogged by inter-band friction which has previously led to the departures of former members Siobhan Donaghy in 2001 and Mutya Buena in 2005.
Donaghy later accused Buchanan of bullying.
In a series of messages on Twitter, Keisha said she was looking forward to the future and said her departure had nothing to do with arguments or bullying.
The singer - who called herself "the feisty, funny, professional, fearless, motormouth", said: "I would like to state that there were no arguments, bullying or anything of the sort that led to this."