He did not say where Weir is going.
Weir, who has co-hosted "Nightline" since 2010, said on his Twitter account that he would be saying "goodbye" on Friday night's program.
Weir helped launch "GMA's" weekend edition in 2004 and was named co-anchor of "Nightline" in 2010.
"Bill’s style is singular; his voice unique; and we will miss him and, yes, his turkey frying safety tips," Sherwood said in a statement."
"Nightline" comes on at 12:35 a.m.
[For the record: And earlier version of this post said "Nightline" airs at 12:35 p.m. It actually comes on at 12:35 a.m.]
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