The 38-year-old actress, who rose to fame as the loveable Stacey on the hit BBC TV show, already has two children with hubby James - three-year-old daughter Eva and one-year-old son Kit.
Joanna shared the news in a typically hilarious way for the star, giving a bit of an insight into how her pregnancy is as an already mum-of-two, and revealing that she's been suffering with the dreaded morning sickness.
She said: 'Some good news! We've got baby number 3 on the way!!!! Morning sickness is a breeze when you're already looking after a 3 and 1 year old!'
Some good news! We've got baby number 3 on the way!!!! Morning sickness is a breeze when you're already looking after a 3 and 1 year old!— Joanna Page (@jopage_) June 18, 2016
Fans have been quick to congratulate the star. One tweeted: 'Congratulations babes! Amazing news! Xx' to which Joanna replied: 'thank you!! I feel sick as a dog and I'm already huge! Hope you're well!! Xxx'
After another fan sent well wishes, the Welsh star responded: 'thank you!! Can't stop being sick and eating! Which is really pleasant! Hope you're well!! Lots of love xxx'
Actor James, who played farmer John Barton on Emmerdale from 2009 to 2012, also shared his excitement on Twitter. 'Great news! Baby number 3 is on the way! Gonna be shifting from man to man marking to more of a zonal system of child control!'
Great news! Baby number 3 is on the way! Gonna be shifting from man to man marking to more of a zonal system of child control!— James Thornton (@JamesThornton_) June 18, 2016
The pair, who married in 2003, have been vocal about their desire to have a big family. Joanna even hinted at being 'addicted' to having as large a family as possible!
'James is one of four, so to him four is the norm. For me one is the norm, but I can see how people get addicted to having babies.'
'I would like to keep going and pop out as many as possible - I only wish I'd started having them at a younger age.'
Congratulations Joanna and James!