Sarah reached out to Girls Aloud bandmate Kimberley last night (17 November) after she announced her exciting news to friends, family and fans on the weekend.
Comparing her congratulatory message to one she gave at the Brit Awards, Sarah - who was responding to happy birthday tweet from Kimbers - joked: "I do believe ANOTHER congratulations is in order for the one and only @KimberleyJWalsh.
"As I said once before when we won our Brits......"ITS ABOUT TIME!!!!" Lots of love to you all babes xxx."
New mum Kimberley revealed on Saturday that she and Justin had got engaged by sharing a picture of her giant ring on Twitter.
Without needing words, Kimberley simply captioned her photo with emoticons of a ring, a love heart and a little family of three.
In September, Kimberley gave birth to her first child with Justin, a baby boy called Bobby Jay.
She has been dating Justin for more than a decade, so Sarah is right, it's about time he put a ring on it!
Celebrity engagements of 2014:
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