Nicola Roberts is ''obsessed'' with Kimberley Walsh's bum.
The Girls Aloud singer wishes she was more curvaceous like her bandmate and admits she couldn't resist ''poking'' her friend when they recently holidayed in Las Vegas for Cheryl Cole's birthday.
Nicola said: ''The problem was, I was next to Kimberly and I'm obsessed with her bum. It's a real issue.
''I was poking it. It's so soft and spongey, I'd love to swap bodies with her. I'd like to be more curvy.''
The 26-year-old star doesn't let her body envy get in the way of their friendship, however, and insists the girls - including Sarah Harding and Nadine Coyle - have all remained close friends despite not having performed together in three years.
Nicola said: ''It's always fun when we're together. We see each other all the time.
''I was with Nadine and Kimberly the other week for dinner.''
The 'Call The Shots' singers are rumoured to be reuniting for the Royal Variety performance this autumn, but Nicola isn't giving anything away.
She said: ''I can't tell you anything! Except it's going to be really fun.''