Torment McFly, say - ultimately Tom Fletcher also joined Busted (9)
I believe the answer is:
martyrdom
'torment' is the definition.
(thesaurus)
'say ultimately tom fletcher also joined busted' is the wordplay.
'say' becomes 'marty' (I can't explain this - if you can you should give a lot more credence to this answer).
'ultimately' suggests the final letters.
'busted' is an anagram indicator.
The last letters of 'tom fletcher also joined' are 'mrod'.
'mrod' with letters rearranged gives 'rdom'.
'marty'+'rdom'='MARTYRDOM'
'mcfly' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for martyrdom that I've seen before include "Death for one's beliefs" , "Death of one dying for their religion" , "suffering" .)