'Sister Wives' star Robyn Brown expecting a girl

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

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

WATCH: 'Sister Wives' Star Robyn Brown Is Pregnant!

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.

Kody had been legally married to Meri, however the two 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. Robyn is also 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 Jan. 7.

Roby and Cody first revealed they were expecting a new baby back in June.