Leah Remini is opening up about her time as a follower of the Church of Scientology as well as her decision to leave the church.

The former “King of Queens” star will sit down for an interview on “20/20”, where she will speak about her experience in the church and how the environment became something she could no longer bear.

"The decision to leave is, you're giving up everything you have worked for your whole life," she said to ABC News' Dan Harris. "I feel that people need to understand this has been my whole life and I want them to understand how it happens."

She continued, "As time goes on, you start to lose touch with the real world. The mindset becomes us against them."

PHOTOS: Celebrities who are outspoken about their religion

Remini also opened up about a famous member of the Church of Scientology — Tom Cruise, who is an outspoken advocate for the church.

"Being critical of Tom Cruise is being critical of Scientology itself. You are evil," she alleged.

The interview comes before Remini, who is currently starring in the TLC reality show “It’s All Relative”, is releasing a new book titled “Troublemaker: Surviving Hollywood and Scientology.”

APP: Download the E! Online app to get the latest celebrity news on the go!

The memoir will be a "moving and eye-opening account" of Remini's 30 years within the church, according to Ballantine Books.

"Bold, brash, and bravely confessional, ‘Troublemaker’ chronicles Leah Remini's remarkable journey toward emotional and spiritual freedom, both for herself and for her family."

Since leaving the church, Remini's daughter was baptized in the Catholic Church where the family celebrated "new beginnings."

"For the record @leahremini and I have always been Catholic," Remini's husband Angelo Pagan wrote after the ceremony. "It was a beautiful experience and our little angel is on her way to a more spiritual existence. God Bless!"

The full interview will air Friday night at 10 p.m. on ABC. Remini's new book will be available for purchase on Nov. 3.

PHOTOS: Stars and their juicy books