NEW YORK (CNN) -- Diane Sawyer will take over nightly news anchor duties for ABC when Charlie Gibson retires from "World News" at the end of this year, a network spokesman confirmed Wednesday.



Charlie Gibson and Diane Sawyer worked together on "Good Morning America."



Sawyer, 63, will be the second woman to be the solo host of an evening newscast for an American broadcast TV network.



Sawyer will take the chair in January, ABC's Jeffrey Schneider said.



Gibson, 66, and Sawyer worked together for years on ABC's morning show -- "Good Morning America" -- before Gibson was promoted over Sawyer to anchor ABC's "World News" in May 2006.



Elizabeth Vargas and Bob Woodruff co-anchored the newscast before Gibson. That duo came to an end after Woodruff was seriously wounded by a roadside bomb in Iraq.



Maria Brennan, president of the Washington-based American Women in Radio and Television organization, called the announcement a "watershed moment" and said Sawyer was the "obvious choice" to take over ABC's anchor chair.



Asked about the significance of two out of three network nightly news anchors being women -- the other being CBS' Katie Couric -- Brennan said, "It comes with some excitement and some glee for groups like ours, who have worked for years to ensure that women have parity with their male counterparts."



"When we get to a point in time when we don't even notice the gender, we can really celebrate," Brennan said.



Sawyer worked for President Richard Nixon in the 1970s, first in his White House press office and later helping him write his memoirs after his resignation.



After a stint with CBS News -- including five years as a "60 Minutes" correspondent -- Sawyer joined ABC News in 1989.



She worked on news magazines for ABC -- including "Primetime Live" and "20/20" -- before being assigned to co-host "Good Morning America" with Gibson in 1999.



CNN's Albert Lewintinn contributed to this report.
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