Black Prince in the end pretty heartless (5)
I believe the answer is:
ebony
'black prince' is the definition.
'ebony' can be an answer for 'black' (I've seen this in another clue). I am not sure about the 'prince' bit.
'the end pretty heartless' is the wordplay.
'the end' becomes 'e' (this might be a standard abbreviation I've not previously seen).
'pretty' becomes 'bonny' (I've seen this in another clue).
'heartless' suggests removing the centre.
'bonny' with its centre removed is 'bony'.
'e'+'bony'='EBONY'
'in' is the link.
(Other definitions for ebony that I've seen before include "Black hardwood" , "Hard wood used for black piano keys and in cabinetwork" , "Very dark black" , "Hard dark-coloured wood" , "Hard block tropical wood" .)