Eagle-eyed viewers noticed the absence during Sunday's special 90-minute episode of the zombie drama, which focused solely on Lennie James' peace-loving character Morgan.
Yeun's name was also removed from the show's closing credits.
The omission fuels further speculation surrounding the fate of Yeun's character Glenn Rhee, one of the few, original, remaining characters to make it to Season 6.
Glenn was last seen on the show Oct. 25 after Michael Traynor's terrified character Nicholas decided to take his own life, bringing Glenn down with him into a crowd of zombies.
The last shot of Glenn showed the fan-favorite hero screaming as walkers appeared to eat him. Since then fan speculation has run rampant online that Glenn may still be alive.
Showrunner Scott Gimple released a statement regarding Glenn's alleged demise on AMC's "Walking Dead" analysis program, "Talking Dead," cryptically stating, "In some way, we will see Glenn -- some version of Glenn -- or parts of Glenn -- again, either in flashback or in the current story, to help complete the story."
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