Studio 10 host Sarah Harris just announced her baby's sex with a cupcake.

Studio 10 host Sarah Harris has revealed she is having a baby boy.

Announcing the news while on air on the program on Thursday morning, Harris said she was most excited that she doesn’t have to “buy to new clothes”, as her son Paul is just 17 months old.

“The tight-arse in me is thrilled I’m having a another boy (he’ll be wearing Paul’s hand-me-downs – woohoo!) but really I just can’t wait to hold that little bubba in my arms. And cake is cake, no matter what flavour the icing!” she wrote on Instagram after the announcement.

In June, the 35-year-old said she and husband Tom Ward were surprised to discover their family would be growing to four a little sooner than they’d planned.

“I’m sick of holding my stomach in,” she told the Channel 10 audience. “I’m having another baby!”

Listen to Mia Freedman interview Sarah Harris on No Filter. Post continues after audio. 

“It was kind of a surprise! Because we were hoping to try again at the end of the year. I’ve been pretty queasy and I’m nervous all of a sudden. And pretty tired. But I’m sort of coming through that part now.”

Baby number two is due in December.