Dressed in a slinky black dress, the pregnant model cradled her baby bump as she took a selfie in a bedroom mirror, while a topless JJ stood by her side.
Posting the snap to Instagram earlier today, Caterina said: "7 months down ... Baby hamblett is almost here!"
Former X Factor star JJ announced on Twitter earlier this month that he was going to be dad, 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."
But the 25-year-old singer recently revealed that he was "nervous" and "terrified" of breaking the news to his fans and even his fellow Union J bandmates, Jaymi Hensley, Josh Cuthbert and George Shelley.
Speaking to the Daily Star (29 September), JJ said: "It was a massive surprise. I did panic because we weren't trying and it came as a big shock. But I think everything happens for a reason so now I can't wait."
JJ, who revealed that he'd known he was going to be a father "for a few months" before he told his bandmates, said: "I didn't want to keep it a secret but I wanted it to be the right time.
"I didn't want to tell them straight after the first single and them start panicking. But they've all been great."
JJ doesn't have to worry about the fan reaction either, as the expectant parents have been sent lots of baby gifts, including bibs, sleepsuits and teddy bears.
Caterina said last week: "Wow! So overwhelmed by all the support , lovely cards and gifts from you beautiful Union J fans today ! This baby is getting spoiled ! #thankyou#loveyouguys."
Union J rose to fame after coming fourth place on The X Factor last year.
Since, the boy band have achieved a top ten hit with their debut single 'Carry You'. Their follow-up single, 'Beautiful Life' will be released next month on 21 October.
The boys will also release their self-titled debut album, Union J on 28 October.
Watch Union J's video for 'Beautiful Life' below:
Check out more stars expecting a baby below:
Copyright: Vimeo / Weiss Eubanks