Covert influencer in loop? (5,6,3,6)

I believe the answer is:

power behind the throne

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

'covert influencer' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'in loop?' is the wordplay.
I cannot quite see how this works, but
'in' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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