Guarantee king’s going to come next (5)
I believe the answer is:
ensue
'come next' is the definition.
(thesaurus)
'guarantee king's going' is the wordplay.
'guarantee' becomes 'ensure' ('ensure' can be a synonym of 'guarantee').
'king' becomes 'r' (r is abbreviation for rex).
'going' is a deletion indicator.
'ensure' with 'r' taken away is 'ENSUE'.
'to' acts as a link.
(Other definitions for ensue that I've seen before include "Follow afterwards" , "Happen - to come later" , "succeed" , "Follow subsequently" , "Result in a particular way" .)