The Larry Sanders Show star fell ill on Thursday (24Mar16), according to, and was taken to a Los Angeles-area hospital, where he died unexpectedly.

A source close to Shandling insists he appeared to be in the best of health hours before his death.

And now, his primary physician has reportedly refused to sign his death certificate because he is unaware of how or why his patient died. TMZ claimed on Friday (25Mar16) that the doctor hadn't seen Shandling in over a year, and was under the impression that he was in good health.

His decision has now triggered an official investigation by the L.A. County Coroner, who will now officially determine the cause of death. It was reported that investigators have taken blood work from the emergency room where Shandling was pronounced dead, and have requested medical records from his doctor.

The news outlet reports that Shandling died from a massive heart attack.

Born in Chicago, Illinois, the comedian became a household name when he guest hosted The Tonight Show Starring Johnny Carson, and was briefly considered as the TV icon's replacement.

He created his own sitcom, It's Garry Shandling's Show, for U.S. cable network Showtime, and then found cult success with The Larry Sanders Show, in which he played a fictional late-night talk show host.

The programme, which ran from 1992 to 1998, scored more than 50 Emmy nominations. Shandling won gold for the series finale, among other accolades.