EXCLUSIVE
Jack Klugman's cause of death was prostate cancer according to the actor's death certificate ... TMZ has learned.
The document also states Klugman died at his home in the San Fernando Valley. His wife Peggy was by his side.
Klugman -- who died unexpectedly on Christmas Eve -- was most famous for playing Oscar Madison on the legendary TV show "The Odd Couple" ... followed by the title role on "Quincy, M.E." in the 70s and 80s.
The actor had already beat cancer once in the 80s -- and although the throat cancer battle cost him his voice, he eventually trained himself to speak again.
Klugman was 90 years old.
They play for opposite teams on television, and last night "Modern Family" stars Eric Stonestreet and Ty Burrell went head-to-head on the sidelines to root for their teams at the Tostitos Fiesta Bowl in AZ.
There is one part of his body that Simon Cowell does not want to expose to the sun -- or photographers -- his luscious hairy man boobs. 
Ariel Winter's about to do something she's never done before -- attend high school like a normal kid, and get this ... she can't wait to go ... TMZ has learned.
Naomi Campbell reportedly suffered a torn ligament in her leg when she was mugged on a street in Paris.
