Updated at 11:50 p.m. EDT
Mei Xiang, the female giant panda at the Washington National Zoo, gave birth to two live cubs on Saturday.
The first cub was born in the afternoon, and the second cub emerged 4 1/2 hours later. Both appear to be healthy, the zoo reports.
Mei Xiang was artificially inseminated in late April and had been monitored since for signs of successful conception. The zoo first detected signs of the pregnancy in July and reported the possible pregnancy on August 10.
Mei Xiang is already the mother of two cubs: Tai Shan, born in 2005 and now living in China, and Bao Bao, born two years ago this Sunday. (Like all giant pandas, Mei Xiang is owned by China. She's on loan to the National Zoo, and the lease requires that her offspring must eventually be sent to China.)
She's also had two pregnancies that ended in heartbreak for panda watchers: a cub that only lived six days, born in 2012, and a stillborn cub birthed immediately after Bao Bao in 2013.
Pandas are notoriously difficult to breed in captivity, and it can be difficult to tell whether a female panda is truly pregnant or just experiencing a pseudopregnancy.
But this time, it was real: Mei Xiang went into labor on Saturday, and the first cub was born at 5:34 p.m. The birth was broadcast live on the internet and has since been posted on YouTube. While panda-lovers were rejoicing over that birth, they had a surprise on their way: the second cub was born at 10:07.
We will have to wait a while for more details. The zoo's veterinarians have not yet separated mother and cubs, and when they do take the cubs aside for examination, it can take some time to determine an infant panda's gender.
At this point, we also do not know the cubs' father. Mei Xiang was inseminated with sperm from two pandas — Tian Tian, also at the National Zoo, who fathered her other cubs, and Hui Hui, a panda in China.
There's one last piece of information that won't be known for a while: the cubs' names. Following tradition, the baby pandas won't be named until they is 100 days old.
News of the birth has caused the National Zoo's Panda Cam to crash for most users. If you're having trouble getting your panda fix, try this: a video of big sister Bao Bao enjoying her first snowstorm this past winter.