Australian pop star has change of heart in prayer (5)
I believe the answer is:
kyrie
'prayer' is the definition.
(type of Christian prayer)
'australian pop star has change of heart in' is the wordplay.
'australian pop star' becomes 'kye' (I can't justify this - if you can you should give a lot more credence to this answer).
'has change' becomes 'varies' (I've seen this in another clue).
'of heart' says to take the centre (I've seen 'heart' mean this).
'in' is an insertion indicator.
The middle of 'varies' is 'ri'.
'kye' going around 'ri' is 'KYRIE'.
Can you help me to learn more?
(Other definitions for kyrie that I've seen before include "First section of Mass" , "- - eleison" , "Part of the Mass" , "Greek prayer" , "First word of Latin Mass" .)