Ultimately becomes excited by butts (4,2)

I believe the answer is:

ends up

'ultimately becomes' is the definition.
(I've seen this in another clue)

'excited by butts' is the wordplay.
'excited' becomes 'up'.
'by' says to put letters next to each other.
'butts' becomes 'ends' (I've seen this in another clue).
'up' put after 'ends' is 'ENDS UP'.

I've seen this clue in The Sunday Times and The Times.

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