Announced Taoiseach perhaps, at opening (8)

I believe the answer is:

premiere

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

I cannot understand how the remainder of the clue works.

(Other definitions for premiere that I've seen before include "Play's first public performance" , "Mere pier (anag.)" , "First screening" , "Leading actress" , "First ever public performance" .)

I've seen this clue in The Irish Times.

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