Charles Gibson, anchor of ABC's World News, announced this morning that he's retiring at the end of the year.

He'll be replaced by Diane Sawyer, the network says.

In an e-mail to colleagues, Gibson says:

It has not been an easy decision to make. This has been my professional home for almost 35 years. And I love this news department, and all who work in it, to the depths of my soul.

It looks like the New York Post broke the news. As it notes:

Sawyer, 63, now becomes the second woman to anchor an evening newscast— joining Katie Couric, who's been anchoring the CBS Evening News since September 2006.

Gibson, 66, has anchored World News since May 2006, when he replaced Elizabeth Vargas and Bob Woodruff, who'd been severely injured by a roadside bomb in Iraq four months before.

As TVNewser faithfully reports each week, the old-guard TV network news shows' ratings go like this: NBC's Nightly News at No. 1; ABC at No. 2; and CBS at No. 3.