Passionate old king was beheaded (4)
I believe the answer is:
avid
'passionate' is the definition.
(I've seen this in another clue)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for avid that I've seen before include "Ardent about diva" , "Greedy - enthusiastic" , "Extremely enthusiastic" , "Burning" , "Greedily eager" .)