Diane Sawyer bade a teary-eyed farewell to her Good Morning America audience this morning (Friday) but assured her viewers that her "heart is smiling." She is due to succeed Charles Gibson as anchor of ABC's World News on Dec. 21. This morning's GMA featured some of the highlights of Sawyer's tenure on the show since 1999. (Joan Lunden, who preceded her, hosted the show for nearly 20 years.) News reader Chris Cuomo, who is also leaving the show (to become co-host of ABC's 20/20 with Elizabeth Vargas), conceded on the air that he didn't have the "emotional depth" for such farewells. On Thursday ABC announced that George Stephanopoulos will be replacing Sawyer on GMA beginning on Monday, while Juju Chang will replace Cuomo.