The 33-year-old Saturdays' singer and rugby star Ben, 29, who are already parents to two-year-old daughter Aoife-Belle, announced they are expecting at the beginning of last month.
UNA FODEN SHOWS OFF GROWING BABY BUMP ON STAGE WITH THE SATURDAYS
Speaking to a British magazine, Una said they're having a boy – and that Ben predicted it.
She said: "Ben was adamant from the moment we knew we'd conceived again that we were having a a boy.
"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 FODEN 'FEELS SEXIER THAN EVER': "I'M NOT BORING BECAUSE I'M MARRIED WITH KIDS"
Speaking recently of their good news, Ben said that he's looking forward to having a son and that Aoife is also getting excited.
He told the MailOnline: "Aoife knows something's going on. Una shows her her tummy and tells her there's a baby in there and she kisses it. She sort of understands. She's really good with other kids. I think she's desperate to have a brother or sister to play with."
Ben also praised his wife for working with The Saturdays throughout both of her pregnancies. He added: "Una's been great. Going on that big tour performing every night on stage is a big ask for someone who is carrying a child so I couldn't be prouder."
THE SATURDAYS: "WE'RE JUST LIKE ANY OTHER WORKING MUMS – YOU MAKE IT WORK"
And it looks like Una won't be letting her husband down anytime soon, as she insisted the rumours of a split for the group are completely false.
She said: "If that was what we wanted, we would be honest and say so. We're always going to be The Saturdays. None of us wants the group to end. So while we'll go off and so our own things, it will always be in conjunction with what The Saturdays have going on. We're definitely not splitting up."