What stimulates announcement of head of state's partner? (6)
I believe the answer is:
fillip
'what stimulates' is the definition.
'announcement of head of state's partner?' is the wordplay.
'announcement of' indicates a 'sounds like' (homophone) clue.
'head of state's partner?' becomes 'philip' (Prince Philip, spouse of the Queen).
'philip' sounds like 'FILLIP'.
(Other definitions for fillip that I've seen before include "Sharp stimulus or flick of a finger" , "Stimulus, quick boost" , "If pill could be used as a stimulant" , "Spur - incentive" , "As tonic" .)