Brandi Glanville is not on Scheana Shay's side -- shocker -- especially when it comes to Lisa Vanderpump.

She was reminiscing about her relationship with LVP to cohost James Maas on the latest episode of the "Brandi Glanville Unfiltered" ... when she recalled that Scheana "wrote horrible things" about Lisa in her memoir.

Brandi jumped to Lisa's defense -- the book came out last July, but better late than never -- and spilled some tea about Scheana in the process.

She recalled Scheana once confessed the SUR server had fallen and knocked her front tooth out ... and Lisa paid for her to get a new one.

And Brandi mused to James that LVP's done a lot for Scheana ... and she shouldn't bite the hand that pays for her teeth!

We've previously reported that Lisa was unbothered by Scheana's shade when we caught up with her in L.A. last year.

And Bravoholics will remember ... Scheana's tooth troubles were a key plot point in the Season 2 premiere of "Vanderpump Rules."

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Fun fact: Brandi appeared on that episode and asked Scheana what happened to her tooth in front of the entire camera crew.

While Brandi still has "real beef" with LVP ... it seems like she'll always have her back against Scheana.