This news has yet to be confirmed by Dillahunt or AMC, but there are possible clues to be found on Twitter, as reported by Uproxx. First, the actor tweeted a picture of his current reading material -- the volume of "Walking Dead" that introduces Negan.
The Spoiling Dead Fans did some sleuthing and found out that "Walking Dead" cast members John Carroll Lynch and Alanna Masterson started following Dillahunt on Twitter, as did "TWD" showrunner Scott M. Gimple -- and he only follows around 300 people. Then, in response to a fan asking if Negan's barbwire-laced bat Lucille looked familiar to him, Dillahunt replied with a cryptic emoji.