Charlie, king beyond doubt (5)
I believe the answer is:
clear
'beyond doubt' is the definition.
(I've seen this before)
'charlie king' is the wordplay.
'charlie' becomes 'C' (phonetic alphabet: alpha, bravo, charlie etc.).
'king' becomes 'lear' (King Lear).
'c'+'lear'='CLEAR'
(Other definitions for clear that I've seen before include "Fine" , "Evident" , "Jump over without contact" , "Unobstructed" , "Empty - vault" .)