Guaranteeing to oust King next? (7)
I believe the answer is:
ensuing
'next?' is the definition.
(I've seen this in another clue)
'guaranteeing to oust king' is the wordplay.
'guaranteeing' becomes 'ensuring' ('ensure' can be a synonym of 'guarantee').
'to oust' suggests deleting specific letters.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'ensuring' with 'r' taken away is 'ENSUING'.
(Other definitions for ensuing that I've seen before include "Immediately following" , "Resulting" , "Following as a consequence" , "This is coming after" , "Following as a result" .)