Dr Jekyll's alternative park? (4)

I believe the answer is:

hyde

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'park?' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for hyde that I've seen before include "Green space in London" , "and 21 Across: Green area in London" , "doctor turned into during work" , "Manchester town, London park" , "First president" .)

I've seen this clue in the Evening Standard.

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