Nadine - who is set to reunite with the rest of the group next year - told heat magazine: "They're not my friends. I don't speak to them or socialise with them. I have my own friends that I've grown up with and the girls are very much my colleagues. I wouldn't socialise with them outside of work."
The pop beauty's relationship with Cheryl is said to be the most strained because while Nadine's solo career flopped, the 'Fight for This Love' singer has flourished on her own, scoring several chart hits, while the band went on hiatus
A source explained: "Nadine and Cheryl have never been close, and they're not about to start now. They are two very different people who were forced upon each other in the band.
"She has always hated the fact that Nadine has a better voice than her and was always given lead vocals, but the sad truth is that having the better voice doesn't matter as Cheryl's had a string of solo hits and Nadine's solo career has fallen flat on its face.
"Nadine is shocked at how well Cheryl has done given her 'lack of talent'. Now she's said openly to her friends that the band needs her for the reunion because she carries a lot of the songs."