Story highlights Mei Xiang gave birth to the first cub Saturday evening

Hours later, she had a second cub

(CNN) And then there were two!

Hours after giving birth to a cub, giant panda Mei Xiang delivered a second one Saturday night, the Smithsonian's National Zoo announced.

"We can confirm a second cub was born at 10:07," the zoo tweeted. "It appears healthy."

Mei Xiang gave birth to the first cub Saturday evening relatively quickly -- an hour after her water broke.

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"The panda team began preparing for a birth when they saw Mei Xiang's water break at 4:32 p.m., and she was already having contractions. The sex of the cub won't be determined until a later date," the zoo said in a news release.

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