'Sister Wives' Star Robyn Brown Expecting a Girl!

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It looks like the Brown family will be welcoming a daughter!

The news that Sister Wives star, Robyn Brown, is pregnant with a little girl was revealed on Sunday's episode of the TLC docu-series, and shared by Robyn's husband, Kody, on Twitter.

"It's a GIRL!" he tweeted. "Yippie!"

Robyn, 37, and Kody, 46, are part of a polygamous relationship, in which Kody is "spiritually married" to three other women as well -- Meri, 41, Janelle, 46, and Christine, 43.

WATCH: Sister Wives Star Robyn Brown Is Pregnant!

Kody had been legally married to Meri, but the two recently got a divorce so that he could marry Robyn, the youngest of his brides.

Between Kody and his four partners, the family has a combined 17 children, and this new addition will make 18.

Kody and Robyn already share one child, 4-year-old son Solomon. She is also the mother three other children -- 15-year-old son Dayton, 13-year-old daughter Aurora and 10-year-old daughter Breanna -- from a previous marriage.

WATCH: Sister Wives Divorce -- Family Has Been 'Legally Restructured'

It was recently announced that Kody legally adopted Robyn's other children after they were legally wed.

The new addition to the Brown family is due on Jan. 7.

Robyn and Cody first revealed they were expecting a new baby back in June. For more on Robyn's pregnancy announcement, check out the video below.