Monarch's powerful blend of tea (9)
I believe the answer is:
potentate
'monarch's' is the definition.
(I've seen this before)
'powerful blend of tea' is the wordplay.
'powerful' becomes 'potent' (similar in meaning).
'blend of' indicates anagramming the letters (I've seen this in other clues).
'tea' anagrammed gives 'ate'.
'potent'+'ate'='POTENTATE'
(Other definitions for potentate that I've seen before include "Mogul" , "authority" , "A monarch or ruler" , "Powerful autocratic ruler" .)