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David Del Rio 's wife, Katherine , is sticking up for her husband amid allegations he sexually assaulted his "Matlock" costar Leah Lewis ... calling Lewis "the most disturbing human being I have ever met."

Katherine posted the fiery message on an Instagram Story Thursday, showing a cropped photo of Leah from a pic of the 28-year-old actress with her mom. Katherine's post has since been deleted.

As we reported yesterday, David was escorted off the Paramount lot last week and kicked off the show as soon as the allegations against him were reported ... according to a source with direct knowledge. David has been accused of committing the unspecified act on Paramount property. Instagram / @leahmlewis

Thursday afternoon, Leah shared a pic of herself embrac

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