Proper to defend a king of myth (5)

I believe the answer is:

priam

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'king of myth' is the definition.
'priam' can be an answer for 'king' (I've seen this before). I'm not sure about the 'of myth' bit.

'proper to defend a' is the wordplay.
'proper' becomes 'prim' (similar in meaning).
'to defend' indicates putting letters inside.
'prim' placed around 'a' is 'PRIAM'.

Can you help me to learn more?

(Other definitions for priam that I've seen before include "Ruler of Troy" , "The last king of Troy, in Greek mythology" , "Father of Paris in Troy" , "Trojan king" , "Old man of Paris" .)

I've seen this clue in The Telegraph.

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