By Brian Stelter, CNN
Diane Sawyer will step down from ABC's flagship nightly newscast, "World News," in August, ABC said Wednesday.
David Muir, the weekend "World News" anchor, will replace her starting September 2.
The announcement ends months of speculation about a transition at ABC's anchor desk.
In a first-of-its-kind arrangement, Muir will not be the main anchor for big breaking news stories or elections - that spot will go to "Good Morning America" co-host George Stephanopoulos, who will have the title "chief anchor."