True: Left decapitated monarch (5)

I believe the answer is:

loyal

I'm a little stuck... Click here to teach me more about this clue!

'true left decapitated monarch' is the definition.
'loyal' can be an answer for 'true' (I've seen this in another clue). I'm not sure about the 'left decapitated monarch' bit.

'true left decapitated monarch' is the wordplay.
'true left' becomes 'l' (common abbreviation. I am not sure about the 'true' bit.).
'decapitated' means to remove the first letter.
'monarch' becomes 'royal' (I've seen this before).
'royal' with its initial letter taken off is 'oyal'.
'l'+'oyal'='LOYAL'

Can you help me to learn more?

(Other definitions for loyal that I've seen before include "Sort of toast" , "Keeping faith" , "Steadfast and true" , "Dependable" , "Faithful to country, cause or friend" .)

I've seen this clue in The Everyman puzzle in The Observer.

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