Under duvet, maybe embracing Romeo? It's natural (6)

I believe the answer is:

inbred

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'natural' is the definition.
('inbred' can be similar in meaning to 'natural')

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for inbred that I've seen before include "Present by nature" , "Lacking genetic variety" , "Was deep in thought" , "4 across" , "too much Montague blood?" .)

I've seen this clue in The Telegraph.

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