Dad-to-be Conor also shared a post and revealed that their little family "can't wait" to meet their little one.
"We can’t wait for the newest member of our little family. @maryviturino18 and I are over the moon and Chanel is very excited to be a big sister," he penned.
Mary and Conor's Bachelor in Paradise were among the first to congratulate the couple on their exciting news.
"So bloody happy for you two!! ❤️❤️❤️ @maryviturino18 @conorjcannin," Glenn Smith commented.
"AHHHHHHH!!!! SO BLOODY HAPPY FOR YOU GUYS!" Alisha Aitken Radburn added.
"Heart is so happy! Congratulations you beautiful people! ❤️❤️❤️❤️❤️❤️," Renee Barrett penned.
Breakout star Niranga Amarasinghe even joked: "Did they cut the contraception supplies to Tasmania?"
Along with Alisha and Glenn, Mary and Conor were the two success stories that emerged from the third season of Bachelor in Paradise.
Shortly after the finale, Mary and daughter Chanel made the move to Hobart, Tasmania where Conor lives and have settled into their new home.
"I think I've always wanted a big family, so we're both keen on the idea. We'll have to see what happens down the track!" Conor said in August.