#lisa vanderpump and her co-stars are returning to Bravo TV tonight in the season eight premiere of "#The Real Housewives of Beverly Hills." Where does Vanderpump's relationship with her longest-running co-star, Kyle Richards, stand?

While Lisa Vanderpump and Kyle Richards started off the eighth season of the reality series in a good place, Vanderpump said during a new interview with Entertainment Tonight that things between them will be tested during season eight. As she explained, they endure a number of “tumultuous” episodes with their co-stars before the drama ultimately ends up affecting their own friendship. As fans saw in the trailer, Vanderpump is seen driving away from a party in tears as a shocked Kyle Richards stands on the sidewalk and watches her go.

“Normally I have my cool, and I kind of lost it that day,” Lisa Vanderpump told Entertainment Tonight on December 18. Continuing on, Vanderpump said that on "#The Real Housewives Of Beverly Hills," fans see all the glamour that the area embodies, as well as the struggles that she and her co-stars have faced. As for Richards, she reflected on the moment as well, telling the outlet that her mouth was hanging open as she watched her co-star and friend drive away because she wasn't used to seeing her let her guard down in such a way.

Lisa Vanderpump's friendship with Kyle Richards is far from perfect

Although Lisa Vanderpump said that she and her co-star have a good friendship, she also noted that, like any relationship, they face problems from time to time. As she explained, there are struggles that she and Kyle Richards go through that are normal for any friends, and ultimately, they always work through their problems and get to a better place.

Richards echoed her friend's statements and noted that they are the closest friends of the entire "Real Housewives of Beverly Hills" cast.

Kyle Richards and Lisa Vanderpump are the 'backbone' of 'RHOBH'

According to Kyle Richards, she and Lisa Vanderpump are the backbone of the show and are also the longest-running original members of the cast. Richards also added that her friendship with Vanderpump has stayed strong throughout their run on the show.

To see more of Lisa Vanderpump, Kyle Richards, and their co-stars, including Teddi Mellencamp Arroyave, Camille Grammer, Dorit Kemsley, Erika Girardi, and Lisa Rinna [VIDEO], don't miss tonight's premiere of "The Real Housewives of Beverly Hills" on Bravo TV at 9 p.m.