Heavy metal, Queen and 'The Boss' (6)
I believe the answer is:
leader
'the boss' is the definition.
(I've seen this before)
'heavy metal queen' is the wordplay.
'heavy metal' becomes 'lead' (I've seen this before).
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'lead'+'er'='LEADER'
'and' is the link.
(Other definitions for leader that I've seen before include "important member of orchestra" , "Head, guide" , "Chief or front man" , "One whose example is followed" , "One is ahead and shows the way" .)