Huell Howser -- Cause of Death Revealed

TV icon Huell Howser -- who hosted KCET's "California's Gold" for 18 seasons -- died after a battle with prostate cancer ... this according to his official death certificate, obtained by TMZ.

Howser passed away at 2:35 AM on January 7 at his home in Palm Springs, CA ... just a short time after he quietly and unexpectedly retired from TV.

According to the death certificate, filed with the Dept. of Health, Huell's remains were cremated ... and his ashes were scattered at sea ... off the coast of L.A. County.