[Update] We reported earlier today, "Panda fans got a double-dose of cute Saturday with the birth of rare twin cubs at the Smithsonian National Zoo in Washington, DC." However, we got an update this evening that the smallest panda has died.

Panda mothers will not nurse a pair of twins, so the zoo's staff had been trying to swap the cubs out every few hours so that the mother is only taking care of one at a time. But mama had strongly resisted giving up her larger cub today. The routine of bottle-feeding the other, while keeping it warm in an incubator, was supposed to increase the "survivability" of both cubs, but did not succeed.

World's First Surviving Panda Triplets Thrive in China

Zookeepers weren't even aware that Panda mom Mei Xiang was pregnant until four days before she gave birth, but this is only the third time in history that a giant panda has given birth to twins in the U.S.

Mei Xiang is also mother to two other living cubs born at the National Zoo–Tai Shan, a male born in 2005, and Bao Bao, who turned two years old on Sunday.

Panda Cub Plays in the Snow for the First Time (WATCH)

It'll still be three or four weeks until the survivor's gender is announced and, following Chinese custom, it won't be named until it is 100 days old.

(WATCH the WJLA News video)  Photos: Smithsonian Institution's National Zoo – Story tip from Julia Freriches

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