Singer appearing embarrassed about their chest? (5)

I believe the answer is:

robin

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'singer' is the definition.
(robins are songbirds)

I cannot understand how the remainder of the clue works.

(Other definitions for robin that I've seen before include "Traditional Christmas card bird" , "So-called outlaw" , "Batman's helper" , "See 7" , "Christmas songbird" .)

I've seen this clue in The Times and The Sunday Times.

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