One of the more memorable characters from Once Upon a Time's first few seasons is coming back for Season 4, though details on his reappearance is being kept under wraps.

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Giancarlo Esposito, who plays the Magic Mirror/Sidney Glass in Once Upon a Time, is set to return for Season 4, according to a new report by TVGuide.com.

Sidney was last seen on Once Upon a Time with his name on the locked door of a hospital in Stonybrooke.

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Esposito is also known more famously for his role as evil businessman Gus Fring on AMC's Breaking Bad, for which he was nominated for an Emmy. He has also starred on such shows as NBC's Revolution.

Going into the fourth season of Once Upon a Time, the series has finished up its Wicked Witch/Zelena (Rebecca Mader) arc and is set to adapt a whole new beloved story. Season 4 is set to feature characters from Disney's massive commercial and critical success Frozen.

Among the characters set to appear in Season 4 are Elsa (Georgina Haig), Anna (Elizabeth Lail) and Kristoff (Scott Michael Foster).

It was also recently announced that Lost actress Elizabeth Mitchell would be joining Once Upon a Time as a character with close ties to Elsa, Anna and Storybrooke as a whole.

Once Upon a Time Season 4 is expected to return in the fall on ABC, though the network has not yet announced a specific premiere date. It will be returning to its regular Sundays at 8 p.m. timeslot.