“Justin and I are so happy to let you all know we are having a baby!!!,” the 32-year-old wrote. “Couldn’t wait to share our lovely news with you all 👶🍼 ❤️.”
Among the first to congratulate the happy couple was Cheryl Cole, who wrote, "FINALLY, I thought at one point I was going to burst 😭😭😭😭😭😭😭😭❤️❤️❤️❤️❤️❤️❤️❤️🍼🍼🍼🍼🍼🍼🍼👶👶👶👶👶👶👶👶."
She also posted a touching message on Instagram to the parents-to-be. "Finally! I am able to share some of the BEST NEWS EVER!!! Kimberley and Justin are expecting their first baby together👶💖💕💞🍼🍼🍼 it has been both one of the most exciting and yet hardest things to keep in!!" she wrote.
"I have watched them grow from strength to strength over the past 10 years! And this is the best bit of it all!!!!!! Aaaaaarrrrgggghhhhhh!! Love you both to absolute pieces CONGRATULATIONS !!"
Nicola Roberts also shared her excitement. "Secrets out!! I am BURSTING with love!" she tweeted. "Kimberley & Justin are having a baby! I am so happy and so literally beside myself with excitement!!!"
Kimberley and Justin have been dating for more than ten years, and live together in North London.
Their announcement comes just two weeks after her former bandmate Nadine Coyle gave birth to her first child, a little girl.
“I’m overjoyed to let you know our little girl is here,” wrote Nadine, who is engaged to American footballer Jason Bell. “She is amazing! I love being a mammy & will fill you all in soon. Love Nadine xxx.”