And now Japanese zoo keepers know why.
It turns out the two polar bears at the Kushiro Municipal Zoo are both girl bears.
Zoo officials say it's often difficult to tell the sex of young polar bears because their long fur doesn't leave much bare on the bears.
Earlier this month, the supposed boy bear was put under an anesthetic for an exam.
It turns he is really a she. Zoo keepers say the popular young polar bear will be allowed to keep his boy's name.