Sources close to the production tell us Vicki, an OG on 'RHOC,' was recently brought back by the network as a guest -- not a full-time housewife or friend -- to film a takedown between her and Tamra.

We're told Vicki was brought by fellow cast member Shannon Beador to a big group outing Thursday -- where all cast members were present -- to confront TJ. Our sources say show producers were hoping the women would hash out their issues and move on ... but, it doesn't seem that happened, 'cause instead we're told the whole night turned into an explosive fight between the trio.

By evening's end, our sources tell us the three ladies left with their friendship more broken than ever before.

BTW ... the Thursday gathering came after Vicki filmed a lunch earlier this week with Shannon and Heather Dubrow -- where Tamra was the hot topic, we're told.

It's pretty shocking to hear how fractured Tamra, Vicki, and Shannon's group friendship has become -- y'know, given how tight they were before TJ dropped out of "Tres Amigas" ... a live comedy project featuring all three women.

On her podcast, Tamra blamed her exit from "Tres Amigas" on scheduling conflicts and a desire not to enable Shannon following her DUI arrest and her frustrations with Vicki and Shannon ... who she thinks have been talking badly about her behind her back.

For Vicki's part, she claimed Tamra blindsided her and Shannon, who have since announced their own comedy tour. Meanwhile, Tamra hit the road to live tape her podcast "Two Ts In A Pod" with cohost Teddi Mellencamp -- who is one of Vicki's sworn enemies.