Family member's crushes? (7)

I believe the answer is:

stepson

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'family member's' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

(Other definitions for stepson that I've seen before include "Spouse's child from previous marriage" , "Subdues" , "second family member" , "Child of a spouse by a former marriage" , "partner's sprog" .)

I've seen this clue in The Telegraph.

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