King – true – not initially kinglike (5)
I believe the answer is:
'kinglike' is the definition.
'king true not initially' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex).
'true' becomes 'loyal' (I've seen this before).
'not initially' means to remove the first letter.
'loyal' with its first letter taken away is 'oyal'.
(Other definitions for royal that I've seen before include "Relating to king/queen" , "Splendid!" , "Of queens, say" , "Kingly or queenly" , "Referring to the sovereign" .)