Crossword Genius

Royal couple misbehave (3)

Ross

I believe the answer is:

err

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'misbehave' is the definition.
Although both the answer and definition are verbs in their base form, I cannot understand how they can define each other.

'royal couple' is the wordplay.
'royal couple' means two replacements for 'royal'.
'royal' becomes 'er' (abbreviation for Elizabeth Regina).
'royal' becomes 'r' (abbreviation).
'er'+'r'='ERR'

Can you help me to learn more?

(Other definitions for err that I've seen before include "Drop a clanger" , "Deviate" , "'to... is human,to forgive divine'" , "Make mistake in Canberra" , "do something you shouldn't" .)

I've seen this clue in The Telegraph.
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