(CNN) -- Who's the daddy? Is it a boy or girl?
The National Zoo in Washington will answer those questions Thursday morning when it announces the gender and paternity of a giant panda cub that was born last month.
"Stay tuned! We're going to announce the sex and paternity of the panda cub tomorrow around 9 a.m.! #cubwatch," the zoo tweeted Wednesday.
The news was greeted by joyous tweets from fans of Washington's celebrity panda, Mei Xiang.
The giant panda mama gave birth to the cub August 23, to the excitement of hordes of fans watching it on public panda cams.
The cub, about the size of a stick of butter, did well and the mother could be seen cradling it in her den at the National Zoo.
But the zoo's second baby watch did not end so well. Mei Xiang's second cub arrived the next day.
She groomed it for 17 minutes before it fell onto the floor of the den motionless, a zoo spokeswoman said. It was stillborn.
On Thursday, the zoo will answer another pressing question about the birth.
Mei Xiang was artificially inseminated by sperm from two different pandas, zoo officials said. One panda is Tian Tian, a 16-year-old, 264 pound male who lives in the same zoo as Mei Xiang. The other potential father is Gao Gao, a 20-plus years old, 174 pound giant panda from the San Diego Zoo. Gao Gao has already fathered five giant pandas.
Speculation in the giant panda community was rampant in the blogosphere.
"Oooh, exciting! Both excellent candidates," Amy Walter from North Carolina tweeted.
Isabel Lara from Washington said she may know who the daddy is.
"You know, I am betting on the San Diego panda ... not sure about gender," she tweeted.
Giant pandas are one of the world's most endangered species.