Diane Sawyer

After estimating she's been on 2,881 shows in 10 years as Good Morning America co-anchor, Diane Sawyer announced on Monday's show that this week will be her last on the morning program.

"You're really giving up your day job, after all this time," co-anchor Robin Roberts said, calling Sawyer "my Thelma. It is so difficult ... Thank you. We're going to do all things just like you this week, we're going to have fun, we're going to look back."

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Sawyer, 63, won't be off the air for long. ABC announced she will start as World News Tonight's new anchor on Monday, Dec. 21; current anchor Charles Gibson will step down Friday, Dec. 18.

Good Morning America will honor Sawyer throughout the week, a celebration that began Monday with the show's news anchor, Chris Cuomo.

"It is amazing, I think to all of us, what we've been able to see you do on this show. It really matters. It makes us all proud," Cuomo said before showing a clip of Sawyer's 2006 interview with North Korean Gen. Ri Chan Bok. However, in a light-hearted video of Sawyer behind the wheel, Cuomo pointed out Sawyer has "has her flaws — some of them, dangerous flaws."

Sawyer's Good Morning America replacement has yet to be named, although ABC's chief Washington correspondent, George Stephanopoulos, reportedly is the front-runner.