25-year-old JJ broke the happy news on his Twitter page on Wednesday (18 September) by writing: "Guys I want you to be the first to know that I've got some big news...I'm going to be a daddy.... :-) :-) wooop x."
And clearly he and Caterina can't wait to be parents.
Yesterday (19 September), the brunette model couldn't resist sharing her baby joy with fans and excitedly posted a sonogram of the unborn child online, along with the caption: "Someone looks extremely comfortable ...Our little monkey ! #babyhamblett #jjhamblett."
She also revealed that she is now part of Mothercare's 'Baby & Me' club, writing: "Just joined the club! Haha! So excited for our little monkey to arrive ! #jjhamblett #mothercare."
Meanwhile, JJ has been getting into the parenting spirit too by buying some children's books to read to his little one.
He uploaded a picture on the Union J Instagram account of himself sitting with his dog and holding up a Winnie The Pooh story and a copy of his group's autobiography.
He joked: "Cant decide what to read lola and the baby??? #harddecision lol x"
Following his announcement on Wednesday, JJ was inundated with congratulatory messages from fellow celebs, fans and his band mates.
One star that was quick to send his best wishes was Marvin Humes, who knows all about being a father after wife Rochelle gave birth to their daughter Alaia-Mai earlier this year.
Marvin tweeted: "Big congrats to @JJUJWorld and Caterina! Amazing news that you're expecting your first baby..it's the BEST feeling ever! X"
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More celebrities with babies on the way in our gallery below!
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