Young Simpson, entitled to 'Sir'? (4)

I believe the answer is:

bart

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'young simpson' is the definition.
(character in The Simpsons)

I can't explain the remainder of the clue.

(Other definitions for bart that I've seen before include "Small title-holder being a brat" , "Branch of Islam" , "Son in The Simpsons" , "Homer's son" .)

I've seen this clue in the Evening Standard.

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