One mate in attire upsetting French queen (5,10)
I believe the answer is:
marie antoinette
'french queen' is the definition.
(I know that Marie-Antoinette is a queen)
'one mate in attire upsetting' is the wordplay.
'upsetting' is an anagram indicator.
'one'+'mate'+'in'+'attire'='onemateinattire'
'onemateinattire' anagrammed gives 'MARIE-ANTOINETTE'.
(Other definitions for marie antoinette that I've seen before include "She lost her head" , "unpopular queen" , "French queen, d.1793" , "Queen, guillotined in 1793" .)