Agreed teen had turned into a reprobate (10)

I believe the answer is:

degenerate

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'reprobate' is the definition.
(I know that degenerate is a type of reprobate)

'agreed teen had turned into a' is the wordplay.
'agreed teen' anagrams to 'DEGENERATE'.
However, I am unsure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for degenerate that I've seen before include "Debauched" , "Get worse" , "sink" , "Reprobate" , "Dissolute" .)

I've seen this clue in The Daily Express.

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