The 29-year-old announced Monday he's expecting a baby girl with his wife, Tori Roloff.
Roloff and Tori are already parents to 2-year-old son Jackson. Roloff shared a slideshow of family photos on Instagram.
"Yay!! Tori and I are excited to announce that Jackson is going to be a big brother to a little sister!! #zandtpartyoffour," he captioned the post.
Tori posted a slideshow of similar pictures on her own account.
"Zachary and I are so excited to announce that Jackson is going to be a big brother! We are expecting a sweet baby girl this November!" she wrote.
"Thank you so much for always supporting our family and loving us!"
Roloff and Tori shared the news just one day after Jackson's second birthday.
FOLLOW REALITY TV WORLD ON THE ALL-NEW GOOGLE NEWS!
Reality TV World is now available on the all-new Google News app and website. Click here to visit our Google News page, and then click FOLLOW to add us as a news source!
Tori marked the occasion Sunday on Instagram after celebrating with family and friends
"Happy birthday to our sweet (not so) baby J! I can not believe I have spent 2 years of my life with this kid. It goes by way too fast," Tori captioned the post.
"Jackson you are so confident and I have loved watching your personality develop. You are becoming so silly and always up for a good time! You are so easy going and smart," she praised her son.
"I pray that you continue to face life head on the way you do and continue to bring smiles to everyone's faces effortlessly."
"I love you so much Jackson! Happy birthday! Can't wait to see what is ahead this year! thank you to everyone who came to celebrate with us and passed along sweet notes to me! #babyjroloff #zandtpartyofthree," the star added.
Roloff, who has dwarfism and stands 4'3" tall, married Tori in July 2015.
The couple confirmed after Jackson's birth in May 2017 their son also has dwarfism.
"[Dwarfism is] part of the whole package of who he is," Roloff told People at the time.
"He's happy and healthy. That's all that matters."
Copyright 2019 United Press International, Inc. (UPI). Any reproduction, republication, redistribution and/or modification of any UPI content is expressly prohibited without UPI's prior written consent.