The 32-year-old's close friend and ex-bandmate Cheryl Fernandez-Versini was quick to support Kimberley by re-tweeting her post.
Bradford-born Kimberley has been dating former Triple 8 singer Justin for over ten years.
The couple welcomed their first child, a little boy named Bobby, on 4 September.
Kimberley and Justin in 2012
Kimberley announced the little one's arrival online, posting: "Our beautiful baby boy Bobby arrived yesterday afternoon 04/09/14 he's perfect."
The new mum was overwhelmed with an outpouring of love and support from her fans, later writing on Twitter: "Thanks for all your lovely tweets about my little Bob's. He is deffo feeling the love."