Attractive woman briefly claims the heart of William Tell (4)

I believe the answer is:

blab

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

I cannot understand how the rest of the clue works.

(Other definitions for blab that I've seen before include "Divulge secret information" , "Spill the beans" , "Give away secrets" , "24 ac secrets in talk" , "Shoot one's mouth off" .)

I've seen this clue in The Independent.

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