It's true it will upset the ingenue (7)
I believe the answer is:
genuine
'it's true' is the definition.
(synonyms)
'upset the ingenue' is the wordplay.
'upset' indicates an anagram.
'ingenue' is an anagram of 'GENUINE'.
'it will' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for genuine that I've seen before include "Authentic; honest" , "Not fake or counterfeit" , "Native" , "'Real, unfeigned (7)'" , "Ingenue - the real McCoy" .)