After confessing to cheating on his wife and a [expletive] addiction, Josh Duggar checked into a "faith-based" rehab, believed to be Reformers Unanimous, a Christian treatment center long supported by his parents.

But the Rockford, Illinois-based facility is hiding a dark sex secret of its own.

Breaking Celebrity News can reveal that a former Reformers Unanimous counselor, Pastor Jack Allen Schaap, was charged with transporting an underage female across state lines for sex.

According to United States District Court documents, the 56-year-old clergyman— who brought the Reformers Unanimous program to his parish, the First Baptist Church of Hammond, Indiana— had an "inappropriate relationship" with an "underage parishioner" referred to as Jane Doe in the summer of 2012.

READ THE SHOCKING COURT PAPERS

"The relationship started when Schaap was counsel