New dad Marvin tweeted, "This morning we welcomed our baby girl Alaia-Mai Humes...Mum is doing great & baby is amazing! We are both overjoyed! Thanks for your love x"
Their little darling made her entrance on Monday morning, a year after the couple wed in a lavish wedding at Blenheim Palace that combined old world glamour with a warm family atmosphere.
Rochelle's bandmates no doubt share her excitement. As the mother of a 14-month-old girl called Aoife Belle, Una Healy understands the emotions she's going through.
Meanwhile, their colleague Frankie Sandford is also pregnant by fiancé Wayne Bridges.
Una loves being a mum as she's explained in her exclusive blog for HELLO! and will have plenty of tips for her friends..
"I worked as far as I could into my pregnancy and returned quite soon after having Aoife but I never sacrificed my family time," the Irish beauty said. "It’s very precious to me.
"I’ve shown Rochelle and Frankie that it is possible to juggle the two."
If anyone can handle the challenges ahead, it's the energetic new mum. The songstress was performing with the rest of The Saturdays right up until the seven-month mark when she took part in a concert at London's G.A.Y nightclub just after her 24th birthday, which was on 21 March.
Even after taking maternity leave because she didn't want to "give birth on stage", Rochelle found it hard to sit still.
"I get that I need to rest but, this is SO not me" she tweeted in frustration. "I hate doing nothing. Gonna be long few weeks #maternityleave. Miss my Sats xx"
She'll also have plenty of help from her devoted husband. Marvin, 28, is due to start a new chapter in his professional life after JLS bow out as a group at the end of this year. He has a weekly Friday night show on Capital FM, as well as being inundated with offers for reality shows.
Amid the changes in his career, the pop hunk has made time to help his wife plan for the little one, accompanying her on shopping trips to stock up the nursery and ferrying her protectively around.
The photogenic duo have been together since early 2010. Two years into their courtship on New Year's Eve 2012, the boyband star proposed the question with a £45,500 heart-shaped ring.