Hard-hearted relative drops in, overwhelming everyone (7)

I believe the answer is:

callous

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'hard-hearted' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for callous that I've seen before include "Insensitive, cruel" , "Heartless" , "Hard-hearted" , "Cruelly unfeeling" , "Cruel and unfeeling" .)

I've seen this clue in The Telegraph.

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