One who unexpectedly turns out successful or beautiful (4,8)

I believe the answer is:

ugly duckling

(Other definitions for ugly duckling that I've seen before include "Swan as unpromising youngster" , "Bird in H. C. Andersen story" , "one succeeding against expectation" , "Hans Christian Andersen cygnet" , "Cygnet (in the story)" .)

I've seen this clue in The Guardian.

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