Former Queen upset business, sacking leader in interim period (7)
I believe the answer is:
regency
'period' is the definition.
(Regency is an example)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for regency that I've seen before include "British period, Eighteen-Eleven to Eighteen-Twenty" , "Period (1811-20) covering The Madness of King George III" , "Old style" , "Interim ruling period on behalf of another" , "Period 1811-1820 in UK" .)