They announced the news on Instagram, both sharing photos with their new daughter.
“Lola Ellis Johnson.. you had us all fooled! Everyone from your Mum, your Nana, the neighbour and even the postman thought you were going to be a boy,” Matty J captioned his post.
“Playing pranks on us all already.. I love it! I also love that I’m now well and truly outnumbered by 3 beautiful and rambunctious girls at home. Welcome to the family.”
The couple are also parents to daughter Marlie-Mae, 20 months.
The surprise of a second little girl was a learning lesson for the new mum.
“I said I would eat my own poop if you were a girl, and yet HERE YOU ARE!,” Byrne captioned the photos.
“Already teaching me the worldly life lessons that come with being a mama – such as, just because I feel something to be true (in my waters) doesn’t mean it is and not to make promises to @matthewdavidjohnson that I 100 per cent do not intend on keeping.”
Johnson and Byrne met on the Australian version of the reality TV franchise in 2017 and welcomed their first child together in June 2019, two months after getting engaged.
The couple announced the news they were expecting a second child in a family photo shared in September.
“Please brace yourself for twice the amount of dad jokes,” Matty J joked with his followers.