"The Real Housewives of Salt Lake City" star Mary Cosby and the church she runs with her husband, Robert Cosby Sr. , are back in the spotlight ... this time accused of being a full-blown cult, according to a bombshell new TLC doc.

TMZ’s got your first look at the wild new trailer -- the three-parter dives deep into Mary’s eyebrow-raising marriage to her step-grandfather, Robert Cosby Sr., and the misconduct claims that dragged Faith Temple Pentecostal Church into one seriously controversial new chapter. Bravo

The docuseries gives the mic to former church members breaking their silence for the first time -- including longtime insiders of Faith Temple -- plus a top cult expert who lays out how tactics of control and loyalty enforcement can keep followers in line. Gallery La

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