As a rank, how can it possibly be royal? (4)

I believe the answer is:

tier

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'as a rank how' is the definition.
I can't tell whether this defines the answer.

'it possibly be royal?' is the wordplay.
'possibly' is an anagram indicator.
'be royal?' becomes 'er' (abbreviation for Elizabeth Regina).
'it' is an anagram of 'ti'.
'ti'+'er'='TIER'

'can' is the link.

Can you help me to learn more?

(Other definitions for tier that I've seen before include "Rite about layer" , "Echelon" , "Level - layer" , "Level of a structure" , "'Level, grade (4)'" .)

I've seen this clue in the Evening Standard.

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