French brat is a cause of controversy (6,8)
I believe the answer is:
enfant terrible
This could be a double definition.
'french brat' is the first definition.
'enfant terrible' can be an answer for 'brat' (I've seen this in another clue). I'm not certain of the 'french' bit.
'cause of controversy' is the second definition.
'enfant terrible' can be an answer for 'cause' (enfant terrible is a kind of cause). I'm unsure of the 'of controversy' bit.
'is a' is the link.
Can you help me to learn more?
(Other definitions for enfant terrible that I've seen before include "nonconformist" , "scamp" , "Unconventional" , "wild child - with 30a" , "one that causes embarrassment" .)