The 33-year-old posted a short video showing her tummy rippling as her new baby kicks.
Saturdays’ singer Una and rugby player husband Ben, 29, are already parents to two-year-old daughter Aoife-Belle.
She and Ben recently revealed the sex of their new baby, admitting it wasn’t what she’d been expecting.
Speaking to a British magazine, Una said: “I was convinced I was carrying a girl, mainly because this pregnancy is so similar to last time.
“I was actually a little bit taken aback when we found out we were going to have a son. But now I’m over the moon and can’t wait to meet our little boy.”
Una might not have been expecting a little brother for Aoife-Belle, but she insisted Ben was ‘adamant’ their second child was a boy.
And she may be on the verge of becoming a mum-of-two, but Una has no plans to slow down her work load any time soon.
The singer has just become a judge on The Voice of Ireland, and she insisted The Saturdays are going nowhere.
“If that was what we wanted, we’d be honest and say so. We’re always going to be The Saturdays. None of us wants the group to end.”