In a manner that causes disappointment or disillusionment; in a way that shatters hopes or false beliefs.
From disenchanting + -ly (adverb suffix); transforms the adjective into an adverb describing how an action is done.
While rare, this adverb appears in literary criticism describing how a story 'disenchantingly' reveals character flaws—it's the adverbial form writers use when they want to describe an emotionally disappointing narrative turn.
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