Nobel Peace Prize winner showing affection to head of state once (9)
I believe the answer is:
kissinger
'nobel peace prize winner' is the definition.
(Henry Kissinger)
'showing affection to head of state once' is the wordplay.
'showing affection to' becomes 'kissing' (kissing is a way of showing someone affection).
'head of state once' becomes 'ER' (Elizabeth Regina, ie Queen Elizabeth).
'kissing'+'er'='KISSINGER'
(Other definitions for kissinger that I've seen before include "Henry __, US Secretary of State under Presidents Nixon and Ford" , "Old statesman" , "Henry --, US diplomat" .)