Remini was part of the church for 30 years, and during a sneak peek of her interview with ABC News' 20/20, she confessed to feeling isolated from the rest of the world.
"The decision to leave is you are giving up everything you have ever known and everything you have worked for your whole life," she explained. "I feel that people need to understand this has been my whole life and I want them to understand how it happens.
"And so as time goes on, you start to lose touch with the real world. The mindset becomes us against them," she added.
She then spoke out about one of the world's most famous Scientologists, Tom Cruise.
"Being critical of Tom Cruise is being critical of Scientology itself. You are evil," she told show's host, Dan Harris. Harris then asked, "If you knew Tom Cruise was watching this, what would you say to him?"
The promotional clip ends there, but Remini is expected to reveal a lot more details about her time in the church during the full interview, which is set to air Friday night at 10/9c on ABC.
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