Tom Bosley died at 83

Tom Bosley:who famously played Mr. Cunningham on "Happy Days" -- died this morning at a hospital in Rancho Mirage, CA ... TMZ has learned.

A rep for the Bosleys tells TMZ Tom "died of organic leads to or specifically, from the short fight with lung cancer."

The rep adds, "In lieu of flowers, the family asks that donations be made to the American Cancer Society."

He was 83 years old.