spoiler alert
US /ˈspɔɪ.lər əˌlɜːrt/
UK /ˈspɔɪ.lər əˌlɜːrt/

1.
a warning that a forthcoming summary of a film, TV program, book, etc., will reveal details of the plot
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Spoiler alert: The main character dies at the end of the movie.
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Before I tell you about the book, spoiler alert, it has a surprising twist.
1.
a warning that a forthcoming summary of a film, TV program, book, etc., will reveal details of the plot
:
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The article began with a clear spoiler alert.
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Always include a spoiler alert when discussing new movie plots.