A scan by zoo vets on Wednesday revealed that Huan Huan, on loan to Beauval zoo in central France from China along with her male partner Yuan Zi, is expecting her first cub.
"It's exceptional. We just exploded in joy as we've been waiting such a long time for this moment," the zoo's communications director Delphine Delord told AFP.
"It also gives us hope for the conservation of pandas, which in nature are in danger of extinction."
Only 19 zoos around the world, outside China, have been allowed to house pandas.
But breeding pandas, in captivity or in the wild, is notoriously difficult. The female panda is only on heat once a year for about 48 hours.
Huan Huan and her beau were brought together in February, with the hope they would mate, but it didn't happen, said Ms Delord.
Since a panda's gestation period is only 50 days, the baby cub is now due on either August 4 or 5, likely weighing in at around just 100 grammes.
If all goes well with the pregnancy and birth, the cub will leave Beauval in the next two to three years to be returned to China.
Last year, zoo officials had been bitterly disappointed when Huan Huan had a fake pregnancy, a fairly common occurrence among female pandas.
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