"Sister Wives" star Maddie Brown is going to be a first-time mother.

The 21-year-old reality star and eldest daughter of Kody and Janelle Brown announced on Monday that she's pregnant and expecting her first child with husband Caleb Brush.

"So happy to announce our little addition!" she captioned a photo of Brush kissing her baby bump on Instagram.

Maddie and Caleb married in Bozeman, Mont., in June after getting engaged in September 2015. The couple told People they are "both really excited and anxious" to welcome a new addition to their family.

"I think every soon-to-be parent is anxious, but we have so much support from both sides of our family," the pair said.

"I think I'll be the disciplinarian parent just because Caleb already has such a soft spot for the baby," Maddie added. "He already has so much love for the baby."

Kody and Janelle, who practice polygamy, are also parents to Logan, Hunter, Garrison, Gabriel and Savanah.

Kody shares nine children with his three other wives, Meri, Christine and Robyn Brown, and adopted Robyn's three children from her first marriage in 2015.

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"We think it would be super cute to have different names for all the grandmas, like oma, grams or babicka. Grandma said differently or in different languages," Maddie told the magazine.

"Ultimately they get to choose what they are called but my dad will probably be grandpa."

Maddie and her family came to fame on "Sister Wives," which will return for a seventh season Nov. 27.

Maddie and several of her siblings revealed on a tell-all special in 2015 that they won't choose to practice polygamy like their parents.