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“Dynasty” actress Catherine Oxenberg is opening up about her fight to save her daughter, India, from alleged sex-slave cult Nxivm — including the moment a friend told her she was in trouble.

“[The friend] was terrified to speak on the phone, she was afraid she was being tapped. And she said to me, ‘You need to save India,'” Oxenberg tells “Dateline NBC” in a newly released clip

from an interview that will air Aug. 6.

“She said they had signed a lifetime vow of obedience to the master.”

India, 26, is a longtime member of self-help organization Nxivm — whose leader Keith Raniere was arrested on sex trafficking charges earlier this year for allegedly turning women within the group into his personal sex “slaves.”

Oxenberg believes India was also part of the “sorority” — where “Smallville” actress Allison Mack allegedly groomed the slaves to pleasure Raniere, keeping them on strict diets and burning his initials into their skin.

India told the New York Times this year that she moved from LA to Nxivm’s headquarters near Albany to take pricey courses from Raniere, who encouraged her to start a vegan catering company.

She has recently been working at East Village vegetarian restaurant PlantMade as a manager, and is reportedly off the restrictive 800-calorie diet.

Oxenberg is releasing a book about her “crusade” to save India next week.