The secret is out ... 'cause "The Secret Lives of Mormon Wives" star Mikayla Matthews is expecting baby number four!

Mikayla just revealed the big news on IG, sharing adorable pics with her hubby Jace and their three kiddos -- Tommie, Haven, and Beckham -- along with a peek at her fourth via an ultrasound scan.

The post is full of heartwarming moments, like Jace gently cradling Mikayla's baby bump and their kids bouncing off the walls with energy and excitement.

Mikayla captioned the pics, "Thought I’d finally announce the next step on my healing journey🤍 can’t wait to love on this baby👶🏼🥹."

Mikayla shared with PEOPLE the news was a complete surprise, especially considering she didn’t think pregnancy was even possible for her due to some ongoing health issues.

She’s got her hands full for sure -- juggling a pregnancy, filming season two of the Hulu series ... and all the drama that comes with it.

But hey, a new baby might just be the thing that keeps #MomTok together!