Emperor is loyal in Spain (11)

I believe the answer is:

constantine

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'emperor' is the definition.
Both the answer and definition are singular nouns.
Maybe there's a link between them I don't understand?

'loyal in spain' is the wordplay.
'loyal' becomes 'constant'.
'spain' becomes 'e' (abbreviation for Espana).
'constant'+'in'+'e'='CONSTANTINE'

'is' acts as a link.

Can you help me to learn more?

(Other definitions for constantine that I've seen before include "First Christian emperor" , "Great man" .)

I've seen this clue in The Daily Express.

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