King leaves great conductor very regally (8)
I believe the answer is:
maestoso
'regally' is the definition.
(musical instruction)
'king leaves great conductor very' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex).
'leaves' indicates named letters should be taken away.
'great conductor' becomes 'maestro' (I've seen this before).
'very' becomes 'so' (I've seen this in other clues).
'maestro' with 'r' removed is 'maesto'.
'maesto'+'so'='MAESTOSO'
(Other definitions for maestoso that I've seen before include "scored majestically" , "performed impressively" , "movement" , "nobly" , "Majestically (music)" .)