Majestically, they could have been stars (5)

I believe the answer is:

tsars

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'majestically they could' is the definition.
The definition suggests an adverb but the answer is not.

'been stars' is the wordplay.
'stars' can be anagrammed to 'TSARS'.
However, I am not sure how the anagram is indicated.

'have' acts as a link.

Can you help me to learn more?

(Other definitions for tsars that I've seen before include "Old Russia's rulers" , "Old Russian rulers" , "Russian emperors" , "Old monarchs" .)

I've seen this clue in the Evening Standard.

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