Chuck Norris' First Wife Dianne Holechek Dead at 84

Dianne Holechek -- Chuck Norris' high school sweetheart to whom he was married for several decades -- has died ... TMZ has learned.

We spoke with Dianne and Chuck's son, Mike Norris, who tells TMZ ... Dianne passed away peacefully at her home in Texas after a long battle with dementia.

Mike says, "We are thankful she is no longer suffering. She was the best, the greatest mom. We were so lucky to have her."

Chuck and Dianne met at a Torrance, California high school in the late 1950s  ... tying the knot in '58 when the two were just 18 and 17 years old, respectively.

They had two children together ... Mike and his younger brother Eric Norris, a former NASCAR driver.

During their years together, Chuck was unfaithful ... fathering a daughter in the early 1960s with another woman while he was serving in the United States Air Force.

Dianne stood by his side during his meteoric rise to fame as a martial arts champion and action star during the 1970s and 1980s ... though they eventually separated in 1988 and divorced the following year.

Dianne was 84.