The U.S. National Zoo's surviving giant panda cub is a boy and was fathered by the zoo's male panda, the zoo said on Friday.

The cub was born on Saturday to Mei Xiang, who is a top tourist draw in the U.S. capital. A fraternal twin died on Wednesday of pneumonia likely caused by inhaling food, the zoo said.

The cubs were sired by Tian Tian, the zoo's male giant panda, the zoo said in a statement. Mei Xiang was artificially inseminated in April using sperm from Tian Tian and from Hui Hui, a panda in China.

The surviving cub is healthy, putting on weight and crying when Mei Xiang tries to leave its den. It weighed 157 grams (5.5 ounces) early on Friday, a 16 percent gain in about 42 hours, officials said.

"We're ecstatic about that," Robert Fleischer, head of the zoo's Center for Conservation and Evolutionary Genetics, said at a news conference.

The father was identified using gene sequencing, the statement said.

The twins' birth captured international attention since giant pandas are among the world's most endangered species.

The new cub will be kept out of public view until January and no name has been determined yet, officials said.

The David M. Rubenstein Family Giant Panda Habitat has been closed to the public since Aug. 20. It will remain closed to create a quiet area for the pandas.

Mei Xiang previously had given birth to two surviving cubs, Tai Shan in 2005 and Bao Bao in 2013. Bao Bao marked her second birthday on Sunday.

Giant pandas, which are native to China, have a very low reproductive rate, especially in captivity. There are about 300 giant pandas in captivity and roughly 1,600 in the wild