Charles Gibson to leave 'World News' Dec. 18

Diane Sawyer will take anchor chair 'soon thereafter'

Charles Gibson will sign off from "World News" on Dec. 18, the newscast's executive producerJon Banner wrote on the "World Newser" blog Tuesday.

"It's that time of year in this great country of ours when we give thanks for family and friends and focus on the things that matter most to us," Banner wrote. "It's no different here in the newsroom, where we are preparing to see our very good friend and anchor off as he begins a new journey."

Gibson announced in September that he planned to retire from the anchor job on "World News."

"We're going to spend a good deal of time during his final week on the air looking back at the stories Charlie covered, hearing again from some of the remarkable people he interviewed, and paying tribute to our friend and colleague, and the enormous contribution he has made to ABC News over the last three decades.

Diane Sawyer, who will succeed Gibson in the anchor chair on "World News," will start "soon thereafter," an ABC News spokeswoman said.