Reality show winners chart their rise to stardom in Dreams That Glitter
The X Factor judge, 25, teamed up with the girls for the launch of Dreams That Glitter at Waterstones flagship store in Piccadilly, London.
Fans had camped out all night to see Cheryl, Sarah Harding, 26, Nadine Coyle, 23, Nicola Roberts, 23, and Kimberley Walsh, 26.
Sarah was later out partying with DJ boyfriend Tom Crane at The Club bar.
SEE PHOTO GALLERY Girls Aloud promote new book Dreams That Glitter>>