Refuse to armour big tank shelling a supreme leader? (5,4)

I believe the answer is:

diana ross

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

'supreme leader?' is the definition.
(I've seen this in another clue)

'refuse to armour big tank shelling a' is the wordplay.
I cannot quite see how this works, but
'big' could be 'os' and 'os' is located in the answer.
'a' could be 'an' and 'an' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

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

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