Keisha Buchanan had a "tense" night out when she ran into former Sugababe bandmate Amelle Berrabah partying with her replacement Jade Ewen.
The girls all attended the American Express My Live Story gala at Abbey Road Studios to see Mark Ronson performing with Simon Le Bon.
An onlooker said: "Keisha arrived two minutes before Jade and Amelle, they stayed in separate rooms for the first hour.
"When they all moved to the main stage to watch the gig, the tension got too much and Keisha made a swift exit soon after the first track."
The concert, which also saw Mike Snow perform live, was held to make the culmination of the My Live Story project.
My Live Story aimed to uncover the UK's best music experiences.
Entrants were invited to share their most unforgettable live music moments by submitting photos or videos of their favourite gig to create a film called Epic.
Mark said: "It's such an honour to play at Abbey Road. And it was great to play there as part of such a great concept. The film was great, the show was great. So thank you."
:: Epic can be seen at channel4.com/mylivestory and will also be aired on Film Four on Saturday November 27.