The ex-Girls Aloud singer was left fuming after Kimberley Walsh and Cheryl Fernandez-Versini failed to inform her about the celebratory bash held for the flame-haired beauty at Hotel Chantelle in Mayfair, London, last weekend.
She vented to The Sun newspaper: ''I didn't get a f***ing invite to Nicola's birthday!''
She added: ''But you know what? I am independent so whatever. I nearly tweeted about it but I thought I better not. If I had an invite I would have gone but I didn't.''
The 33-year-old singer also hinted her other bandmate Nadine Coyle, who now lives in Los Angeles following the band's split in 2013, wasn't invited to the party either.
She explained: ''Nadine lives in LA, the other three do their own thing and that's just how it is.
''You have got to remember the girls and I spent so much time together when we were in the band.''
But, despite complaining about not being invited to the bash, the blonde beauty failed to even send Nicola many happy returns because she didn't know it was her birthday.
She said: ''I didn't even know it was Nicola's birthday so I definitely didn't wish her a happy birthday.''
Meanwhile, Sarah has admitted her former bandmates' behaviour has meant a reunion for the band has now been struck off the cards for the foreseeable future.
She explained: ''Relations were good between us until I didn't get an invite. I can't see a Girls Aloud reunion happening any time soon, let's put it that way.''
The young artist urges fans to vote like their lives depend on it.
Billie Eilish is back with possibly her most chilled out song yet. 'My Future' comes alongside a melancholy animated video starring Billie herself.