Mad monarch in furtive look we hear (4)

I believe the answer is:

lear

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'mad monarch' is the definition.
'lear' can be an answer for 'monarch' (King Lear). I'm not sure about the 'mad' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for lear that I've seen before include "Tragic king in play" , "tragic hero" , "See 27 Across" , "Lesson" , "Mad king" .)

I've seen this clue in The Sun.

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