Lisa Vanderpump Is the Latest 'RHOBH' Star to Question Yolanda Foster's Lyme Disease

Yolanda Foster is the latest Real Housewives star to be in the hot seat.

After the ladies of Orange County went several rounds over Brooks Ayers’ cancer claims this past season, the housewives of Beverly Hills are turning their sights on Foster, who suffers from Lyme disease.

“I don't quite understand what's wrong with her,” RHOBH star Lisa Vanderpump says in a clip from the show’s sixth season premiere. “I don't know if it is Lyme disease, but I'm not criticizing her - I'm just questioning it.”

WATCH: Yolanda Foster's Emotional Battle With Lyme Disease: 'Many Nights I Wished to Die'

After the ladies of Beverly Hills appeared to be skeptical of Foster’s health claims in the trailer for the upcoming season, which kicks off Dec. 1, ET went straight to the source, asking RHOBH star Kyle Richards for her take.

"I think for a lot of people it's very confusing," Richards explained to ET. "A lot of the things she's gone through and the treatments she's done, for some of the cast members they were questioning exactly what she was doing and exactly how sick she was. It was not a good situation."

According to Richards, the ladies have their reasons for questioning Foster. She revealed that “some things came up that made some of the Housewives question exactly what was really going on," but insisted that fans will have to watch the upcoming season to find out the specifics.

WATCH: Kyle Richards Says 'RHOBH' Co-Stars Are Questioning 'Exactly How Sick' Yolanda Foster Is