One earl upset former queen (7)

I believe the answer is:

eleanor

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

'former queen' is the definition.
'eleanor' can be an answer for 'queen' (I've seen this before). I am unsure of the 'former' bit.

'one earl upset' is the wordplay.
'upset' indicates anagramming the letters.
'one'+'earl'='oneearl'
'oneearl' anagrammed gives 'ELEANOR'.

Can you help me to learn more?

(Other definitions for eleanor that I've seen before include "Wife of F. D. Roosevelt" , "- - Rigby: Beatles song" , "Wife of Henry II" , "Franklin D. Roosevelt's wife" , "Real one (anag) - girl's name" .)

I've seen this clue in The Telegraph.

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