DNA tests conducted on the still unnamed twin giant panda cubs at Toronto Zoo have found the oldest of the pair is male and the slightly younger one is female.

Zoo officials say they took swabs from the cheeks of both panda cubs on Jan. 28 and drove the samples to the Natural Resources DNA Profiling and Forensic on the campus of Trent University in Peterborough.

Using protocols devised by researchers at the Smithsonian Conservation Biology Institute in Virginia, the tests found that the first panda cub (born 13 minutes before his sister) is male and the second one is female.

“The Toronto Zoo is grateful for the ongoing collaboration with the Smithsonian National Institute as we work together and share critical learnings through the giant panda conservation breeding program,” Maria Franke, Curator of Mammals at the Toronto Zoo, said in a news release.

The cubs were born in the early hours of Oct. 13 to mother Er Shun. The cubs’ father is not yet known.

Er Shun and male panda Da Mao arrived at the Toronto Zoo from China in 2013. They are expected to remain at the zoo until 2018, when they will move to the Calgary Zoo.

Toronto Zoo spokesperson Amanda Chambers said the zoo has not been given permission to determine the cubs’ paternity, as that will be determined only when Er Shun and Da Mao are returned to China in 2023.

The panda cub births are the first of their kind in Canadian history.

The Zoo says it will make a special announcement concerning the cubs’ names on Monday.