Former Scientology Executive and Outspoken Critic Mike Rinder Dead at 69

Scientology Critic Mike Rinder Dead at 69 ... Wrote Tell-All Book About Religion

Mike Rinder -- a former higher-up in Scientology who became an outspoken critic of the religion -- has died ... according to an Instagram post from his wife.

Christie King Collbran revealed the news in an emotional Instagram post Sunday ... saying she feels sadness and pain at his passing though his courage and integrity will continue to inspire many for years to come.

Collbran says Rinder was a stable force in the lives of those who knew him ... before adding the "world will remember you."

Christie did not comment on a cause of death ... though last year Rinder announced he was fighting esophageal cancer.

Included in the post is a message Christie says Mike gave her before he died. It reads, in part, "I have been lucky — living two lives in one lifetime. The second one the most wonderful years anyone could wish for with all of you and my new family!"

He adds, "My only real regret is not having achieved what I said I wanted to — ending the abuses of Scientology, especially disconnection, and seeing [my son] Jack into adulthood. If you are in any way fighting to end those abuses please keep the flag flying — never give up."

If you don't know, Rinder was raised as a Scientologist in Australia ... and, after high school, he says he signed a "billion-year" contract with the org. to enter its inner circle.

Rinder was the international spokesperson and the head of its Office of Special Affairs for Scientology ... though he began blowing the whistle on the organization's alleged abuses in 2007.

He penned the book "A Billion Years: My Escape From a Life in the Highest Ranks of Scientology" ... in which he claimed the church grew concerned about Tom Cruise's loyalty during his marriage to Nicole Kidman.

Later, Rinder cohosted "Scientology and the Aftermath" -- the Emmy-winning series all about Scientology -- with Leah Remini which aired its first season 2016.

On their website, the Church of Scientology has posted, "Mike Rinder is not a credible source concerning Scientology. He has not stepped inside a Church in nearly a decade. The Church expelled him for malfeasance and has had nothing to do with him since."

We've reached out to the Church of Scientology ... so far, no word back.