See who it is after the jump (spoiler):
The star is Whoopie Goldberg, and she will be playing the White Rabbit’s wife.
No, she won’t be hopping around in a bunny suit. She’s just going to be providing the voice of the rabbit, who presumably will be a CGI character like her husband.
This will happen, according to TV|Line, during the eighth episode of the season, and Mrs. Rabbit will appear in two timelines — present and flashback.
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