Brandi Glanville told ET it breaks her heart to see the women of The Real Housewives of Beverly Hills attack her friend Yolanda Foster over her Lyme disease diagnosis, which some have questioned.

"I'm livid, honestly," Glanville said at The Real Housewives of Beverly Hills season six premiere party in Los Angeles on Thursday. "Outside of filming, they don't know her. When we're not filming, I hang out with Yo."

WATCH: Yolanda Foster's Emotional Battle With Lyme Disease

Glanville shared that for the past three years since Foster's diagnosis, she has watched her struggle. According to Glanville, there were days when she had to help Foster get dressed because "she couldn't move."

"I have this passion in my gut, and she's like, 'Don't fight for me.' She doesn't want me to. She's like, 'Keep it classy,'" Glanville said. "It hurts me. It hurts my heart to see these women do this to her."

RHOBH star Lisa Vanderpump told ET that she questioned the severity of Foster's illness, but never accused her of lying about being diagnosed with Lyme disease.

WATCH: David Foster Says Wife Yolanda 'Is Doing the Best She Can' Battling Lyme Disease

"Of course we had questions, but we never questioned that she was actually, authentically sick. That's very different," she said. "Everybody had different feelings, I think. I know Kyle [Richards] and I thought, very much, it was authentic, but wondered what was going on with her, really. As I said, I had questions about it, but never questioned the fact that she actually had Lyme disease. I saw that for myself how she didn't look good and was really not herself."

Camille Grammer, who underwent a radical hysterectomy in 2013 after being diagnosed with cancer, stood by Glanville, taking Foster's side in the squabble.

"From the first episode that we've watched, I don't like them questioning anybody's illness," she told ET. "I just don't like it, and I support Yolanda on that. I mean, I feel for her. I empathize with her, because I've been through something very similar and I wish her the best."

Foster herself seemed to be the least bothered by the attacks.

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

"I just let it roll off my back, because I have nothing to prove to anybody except to myself to find a cure for a disease that I've been battling for four years," Foster said. "To be honest with you, it doesn't faze me. I've heard it for so many years now that it goes in one ear and out the other. I just have a very laser-beam focus, and all I want to do is get to the finish line, get my brain back and teach the world a lesson about Lyme disease, and that's my journey today."

The Real Housewives of Beverly Hills airs Tuesdays at 9 p.m. ET/PT on Bravo.