Taking collagen daily may reveal an ulterior motive! (6,6)

I believe the answer is:

hidden agenda

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'ulterior motive' is the definition.
(I've seen this in another clue)

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(Other definitions for hidden agenda that I've seen before include "Concealed intentions" , "followed in secret meeting?" , "covert plan" , "Undisclosed reason" , "Sub-text, unstated objective" .)

I've seen this clue in The Telegraph.

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