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Shake Shack unveils its mystery chicken item

The secret's out.

Known for his hamburgers and custard, Shake Shack on Tuesday debuted the ChickenShack, a crispy all-natural and antibiotic-free chicken breast with lettuce, pickles and buttermilk herb mayo. Starting July 7, the sandwich will be available exclusively in its Brooklyn locations for a limited time.

The new item is the chain's first ever chicken sandwich. Previously, the only chicken dish available had been the chicken dog, a hot dog made with chicken, apple and sage sausage.

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The move follows a trademark filing of the term "chicken shack" in April by a subsidiary of the chain. This news sent the restaurant's stock surging, hitting an all-time high of $96.75 on May 22. Since then, its shares have sunk. Shares received a further pounding Tuesday after Morgan Stanley analysts downgraded the stock, sending it down nearly 10 percent.

Shake Shack's foray into a chicken sandwich comes as chicken chains Bojangles' and privately held Chick-fil-A posted strong growth with poultry-packed menus.