Gao Gao (via San Diego Zoo)

Researchers from the Smithsonian and Chinese panda facilities performed multiple artificial inseminations last weekend on the National Zoo’s femalMe giant panda, Mei Xiang. But, it turns out, that the zoo’s resident male giant panda, Tian “Weakly Loaded” Tian, wasn’t the only sperm donor.

According to a fairly graphic news release from the zoo this afternoon, researchers also used a semen sample from Gao Gao, a male giant panda at the San Diego Zoo. Tian Tian was the sole donor on the first insemination procedure, in which scientists used a frozen sample as well as fresh material collected as the zoo prepared the pandas for breeding last week.

On the second go-round, though, it was a joint effort. Mei Xiang was injected with both a sample from Gao Gao, as well as a 2003 vintage dose from Tian Tian. It’s actually the second time the National Zoo has used sperm from the West Coast panda on Mei Xiang; he was the donor for an unsuccessful insemination effort in 2007.

Tian Tian has one cub—Butterstick—to his name. But Gao Gao has quite the progeny; in his years at the San Diego Zoo, he has sired five cubs, most recently Xiao Liwu, born last July.

If Mei Xiang gets pregnant from these insemination attempts, the National Zoo says it will perform a paternity test. And, just based on history, the new cub will likely tell Tian Tian in panda-ese, “You’re not my real dad!”

In the mean time, the National Zoo’s panda exhibit re-opened yesterday, and zoo officials say Mei Xiang and Tian Tian have “recovered from the procedures.”