Mutya Keisha Siobhan [MKS] partied with Adam Lambert in Los Angeles on Monday (15.07.13).

The pop group - which is comprised of the original Sugababes lineup; Mutya Buena, Keisha Buchanan and Siobhan Donaghy - caught up with the new 'Glee' star while in the city to shoot the video for their single 'Flatline' and he was full of praise for the ''smart, real ladies''.

Adam wrote on Twitter: ''@MKSOfficial I love u all! Such down to earth, smart, real ladies!! What a pleasure!

''Oh and since I was kickin it w the OG Sugababes @MKSOfficial ... I wanted to letchoo LamBrits know how obsessed I am with @Skins (sic).''

The trio were equally happy to see Adam, and posted a picture on their Instagram page with the caption: ''A perfect evening with the one and only adamlambert #MKSinLA (sic).''

MKS were spotted filming the video for their single 'Flatline' - which they wrote themselves - in various LA locations including Venice Beach on Tuesday (16.07.13).

While Keisha previously admitted it was ''weird'' being back together with Siobhan and Mutya because she hadn't seen them for so many years after the pair quit the Sugababes in 2001 and 2005 respectively, she has also called the reunion ''amazing''.

She said: ''For me personally, from the outside, I have never seen Mutya and Siobhan together since we were 15 or 16. To see them years on as grown women talking was just weird. It's been weird adjusting to it. But it's been amazing being back together, and writing together.''