Fate one’s suffered supporting king (6)
I believe the answer is:
kismet
'fate' is the definition.
(I know that kismet is a type of fate)
'one's suffered supporting king' is the wordplay.
'one's' becomes 'i's' (Roman numeral).
'suffered' becomes 'met' ('meet' can be a synonym of 'suffer').
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'king' becomes 'K' (chess abbreviation).
'is'+'met'='ismet'
'ismet' after 'k' is 'KISMET'.
(Other definitions for kismet that I've seen before include "fortune" , "Turkish fate, destiny" , "Will of Allah" , "Destiny; 50s musical" , "lot in life" .)