Diane Sawyer is "stepping aside" as host of ABC's World News, the network announced Wednesday.

Sawyer will be replaced starting in September by weekend and fill-in host David Muir.

An ABC News executive, quoted by the New York Daily News, praised Sawyer for her work on the show, which included being the first female to ever win a Sweeps month when her broadcast finished first in the Adults 25-54 demo:

“As much as she loved leading World News to new heights — with so much important, brilliant and impactful reporting and a number one finish in the May sweep — Diane decided that now is the moment to concentrate full time on tackling big issues in new ways,” ABC News chief James Goldston told staffers Wednesday morning in a memo obtained by The News.

Sawyer's win in May was the first Sweeps win for ABC news in six years. As host, her show regularly finished behind NBC Nightly News with Brian Williams, but ahead of CBS's broadcast anchored by Scott Pelley.