Loni Anderson’s cause of death has been revealed … and she died from an aggressive form of cancer, TMZ has learned.

According to Anderson’s death certificate, obtained by TMZ, the veteran actress passed away from metastatic uterine leiomyosarcoma … a rare cancer that often starts in the uterus and can spread to other parts of the body. It is an extremely rare form of cancer.

Loni died Sunday at a Los Angeles hospital following what her longtime publicist, Cheryl J. Kagan, described as a “prolonged” illness.

Loni’s personal life also made headlines — especially her high-profile marriage to Burt Reynolds. The two tied the knot after costarring in the ’83 comedy “Stroker Ace,” but split five years later.

She was 79.