Distressing experience of king imprisoned in old Kent town (6)
I believe the answer is:
ordeal
'distressing experience' is the definition.
(I've seen this before)
'king imprisoned in old kent town' is the wordplay.
'king' becomes 'R' (abbreviation of Latin rex).
'imprisoned in' indicates putting letters inside.
'old' becomes 'o' (abbreviation).
'kent town' becomes 'deal' (I've seen this before).
'o'+'deal'='odeal'
'r' going into 'odeal' is 'ORDEAL'.
'of' is the link.
(Other definitions for ordeal that I've seen before include "Disturbing experience" , "Difficult or arduous experience" , "Severly trying experience" , "Suffering - trial" , "A tough time or hardship" .)