Crossword Genius

Separated himself — at heart is a rogue (4)

Ross

I believe the answer is:

heel

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

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

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(Other definitions for heel that I've seen before include "Untrustworthy person" , "One of the crusty ends of a loaf" , "See 1 down" , "Spur" , "Call to dog" .)

I've seen this clue in The Hindu.
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