Former monarch accepts note from Islamic chieftain (4)
I believe the answer is:
emir
'islamic chieftain' is the definition.
(I've seen this before)
'former monarch accepts note' is the wordplay.
'former monarch' becomes 'ER' (Elizabeth Regina, ie Queen Elizabeth).
'accepts' is an insertion indicator.
'note' becomes 'mi' (as in do-re-mi).
'er' going around 'mi' is 'EMIR'.
'from' is the link.
(Other definitions for emir that I've seen before include "Middle-Eastern ruler" , "Title of various rulers; I'm ER (anag.)" , "Arab chieftain" , "Eastern title" , "Top man" .)