The 37-year-old actress announced the news in an Instagram post Monday, saying it was "an absolute thrill" to serve as host on the NBC reality competition for two seasons.
"I have some news to share: I will not be returning to the show as host for season 3. But! I won't be able to stay away for long, and plan to return to mentor contestants as much as possible," Dewan wrote.
"It has been an absolute thrill to be a part of this incredible, groundbreaking show from the very beginning, and I am forever grateful to my @nbcfamily, @jlo, @derekhough @neyo and everyone involved in this journey," she added, referencing "World of Dance" judges Jennifer Lopez, Derek Hough and Neyo.
Dewan didn't offer an explanation for her departure, but did tease exciting news to come.
"Can't wait to share more news with you soon. Much love to everyone," she said.
Dewan confirmed her exit in a tweet to a fan Tuesday.
"I will be back season 3 for mentoring on and off," she wrote.
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