Worried, interrupting king's supply (5)
I believe the answer is:
cater
'supply' is the definition.
(I know that supply can be written as cater)
'worried interrupting king's' is the wordplay.
'worried' becomes 'ate' (something worrying may eat someone up).
'interrupting' means one lot of letters goes inside another.
'king' becomes 'cr' (short for Carolus Rex, King Charles in Latin).
'ate' inserted inside 'cr' is 'CATER'.
(Other definitions for cater that I've seen before include "Provide service for like grocer" , "Provide for, supply" , "Supply provisions" , "Provide services, food or entertainment" , "Provide what is needed or wanted" .)