The cruel Mr Green (9)
I believe the answer is:
heartless
'the cruel' is the definition.
(I've seen this in another clue)
'mr green' is the wordplay.
I cannot really understand how this works, but
'mr' could be 'les' and 'les' is located in the answer.
The remaining letters 'hearts' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for heartless that I've seen before include "That's very cruel" , "insensitive" , "Without pity or feeling, being defective in cardiac way" , "with no concern for others?" , "Lacking all feelings" .)