Chap brought up in the heart of Paris (3)
I believe the answer is:
ira
'chap' is the definition.
'brought up in the heart of paris' is the wordplay.
'brought up' is a reversal indicator (in a down clue, letters go up).
'in the' becomes 'aslarge*' (I've seen this before).
'heart' means to look at the middle letters.
'of paris' becomes 'ri' (I am not sure about this - if you are sure you should believe this answer much more).
The centre of 'aslarge' is 'a'.
'a'+'ri'='ari'
'ari' backwards is 'IRA'.
Can you help me to learn more?
(Other definitions for ira that I've seen before include "Illegal organisation, initially" , "George 13 down's brother" , "Militant Irish nationalist organisation" , "Brother of George Gershwin" , "nationalists" .)