No mere king penguin (7)

I believe the answer is:

emperor

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

This might be a double definition.

'no mere king' is the first definition.
'emperor' can be an answer for 'king' (I've seen this before). I'm unsure of the 'no mere' bit.

'penguin' is the second definition.
(emperor penguin is a kind of penguin)

Can you help me to learn more?

(Other definitions for emperor that I've seen before include "Penguin of largest known species - a great ruler" , "He rules over several states" , "chap such as Charlemagne" , "Sovereign - ruler" , "Roman leader" .)

I've seen this clue in the Evening Standard.

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