HOLLYWOOD — Australia’s Nine network ain’t big enough for the both of them — and it’s CEO David Gyngell who has decided to leave.

The exec Monday threw in the towel at Nine, the flagship terrestrial channel of Kerry Packer’s Publishing and Broadcasting, after learning on Friday that TV vet Sam Chisholm was on his way back to PBL as exec director of television interests.

“I was simply not prepared to allow my position to be rendered untenable by what I regard as increasingly unhelpful and multilayered management systems,” Gyngell said.

He has been under increasing pressure to push up ratings after rival Seven’s fortunes soared on the back of “Desperate Housewives” and “Lost.” However, Gyngell, who is Kerry Packer’s godson and a school friend of Packer’s son James, has been barraged with conflicting advice about how to do that from Packer pere (PBL’s major shareholder), Packer fils (exec chairman) and CEO John Alexander.

Gyngell, who took the top job last June, said he was not forced out, but added: “Without the absolutely and unmistakably clear mandate required by all CEOs to properly run any major business, I believed it was in my best interests to move on.”

Chisholm was Nine’s CEO from 1975 to 1990 before joining Rupert Murdoch’s British satcaster BSkyB as its CEO.

He returned to Australia in 2000 and was chairman of pay TV platform’s Foxtel from 2001 until March this year. He has been a director of PBL since September.

Chisholm’s appointment takes effect immediately; he will report to Alexander.

PBL will begin the search for a Nine CEO immediately.

Gyngell — whose father, Bruce Gyngell, was the first face on Australian television in 1956 — did not reveal future plans..

(Wire services contributed to this report)