The long-awaited birth of a new panda cub in Washington came to a clandestine end Sunday night, when the National Zoo’s female giant panda suddenly went into labor in the dark of her den, the zoo announced early Monday.

Mei Xiang, the Zoo’s female giant panda, gave birth to the cub at 10:46 p.m. Sunday. Zoo staffers were not certain that Mei Xiang was even pregnant until they heard noises of the delivery and, eventually, the cub.