Millie Bobby Brown Surprises Fans With Performance of Katy Perry's 'Firework' at Argentina Comic Con

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Millie Bobby Brown is full of surprises!

The 13-year-old actress shocked fans as she sang Katy Perry's "Firework" at Argentina Comic Con in Buenos Aires on Friday.

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Brown first opened up about her Stranger Things character, Eleven, and the show's second season, before treating the audience to performances of both "Ave Maria" and "Firework."

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The British actress also took to Instagram to share pics from the event -- and the massive crowd that showed up to see her.

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ET caught up with Brown in January, where she opened up about her next role in the upcoming Godzilla sequel, King of Monsters, but with her talent for singing, we wouldn't be surprised if a musical followed.

See more in the video below.