Sister Wives fans are learning more about what led to the end of Janelle Brown's relationship with Kody Brown.

In fact, the season 18 trailer for the long-running TLC series, released July 13, sees tensions between the now-former couple reach a boiling point during a particularly heated argument.

As Kody questions his partnership with Janelle, she fires back and suggests they're both to blame for their marriage not working out.

"This is not only me, Kody," Janelle says in the clip. "Don't you dare point your finger at me." 

Their conversation comes to a head when Janelle tells Kody, "Shut your f--king mouth and let me talk to you for a minute," prompting him to storm out. As he leaves, she grabs his sleeve and asks him to stay and talk. However, Kody shrugs her off and says he's done listening to her. 

"OK, so we're done?" Janelle replies. "F--k you." 

However, this fight wasn't the only sign their relationship was over. Earlier in the sneak peek, viewers see Janelle question where she and Kody stand.

"Do you really want to still have a plural family?" she asks him. "Sometimes I can't tell."

And at one point, Janelle tells fellow Sister Wives star Christine Brown—who announced her breakup with Kody in 2021 and is now engaged to David Woolley—that she's ready for a change. 

"I'm growing, and I need something different," she says. "Like, I don't want to be married anymore."

Janelle and Kody revealed their separation after nearly 30 years of marriage on last season's Sister Wives: One on One special, which premiered in December. However, Kody's relationships with Janelle and Christine weren't the only ones to come to an end as the new trailer also shows his fallout with Meri Brown.

In one instance, followers see her having a discussion with her Sister Wives costar Robyn Brown. "There's no question Robyn," Meri says. "He's done with me." 

And eventually, she determines she's moving on.

"I just wanted to let you know I'm not gonna be around," Meri—who announced her split from Kody in January—tells him and Robyn. "It's not what I want."

However, a devastated Robyn explains being a part of a plural family is what she wanted, saying through tears, "I wanted to sit on a porch with my sister wives with our kids and our grandkids."

Kody legally wed Meri in 1990 before going on to also tie the knot with Janelle in 1993 and Christine in 1994. He then divorced Meri so he could legally marry Robyn in 2014. However, Kody still considered himself spiritually married to Meri, Janelle and Christine at the time.

As for how Kody—who has 18 children in total from his relationships with Meri, Janelle, Christine and Robyn—feels about how much their family has changed? 

"I worked so hard to do what was right," he said in the trailer during a confessional. "And when you lose that, well, I should just be the devil I think I am now." 

Season 18 of Sister Wives premieres Sunday, Aug. 20 at 10 p.m. ET/PT on TLC.