'Vanderpump Rules' Returning With All-New Cast for Season 12

Pour one out for the OG stars of "Vanderpump Rules" ... Bravo just announced they're rebooting the entire cast for season 12 of the reality show.

The network tells TMZ ... Lisa Vanderpump will be back for the new season, but will be surrounded by a new group of staffers who work at her West Hollywood hot spot, SUR.

Season 12 returns to the show's original formula, which takes viewers back inside LVP's many restaurants -- where several hookups, feuds and drama are known to unfold.

Sources connected with the show tell TMZ ... stars Tom Sandoval, Tom Schwartz, Ariana Madix, Scheana Shay, James Kennedy, Katie Maloney, and Lala Kent were notified of this decision by production last night.

We're told most of the cast wasn’t too surprised by the new direction ... especially after the show was put on pause back in April.

Despite the shakeup, our sources say the OG stars will still have a home at the network ... as there will be other avenues for them to explore within the Bravo/NBC universe. We're told Lala, Scheana (as well as hubby Brock Davies), and Schwartz are all making appearances on season 2 of "The Valley" -- a spin-off already starring other 'VPR' alums.

TMZ broke the story ... production had picked up cameras in September to film new faces, all of whom were SUR-vers at Vanderpump's business. At the time, sources said the footage was meant for a new project ... but it's clear Bravo decided to pursue this cast over the OGs for season 12.

Fans will get a chance to say goodbye to original SUR-vers, however ... a retrospective special will drop ahead of the new season.