The first tiger to be born at London Zoo in 17 years has died at two weeks old after drowning in a pool outside its den.
Staff at the zoo were left "heartbroken" after the cub was discovered dead at the weekend.
Keepers noticed they could not see the cub on the cameras in the den and raised an alarm.
They later discovered the cub at the edge of a pool. A post-mortem showed the cub had drowned but it is not clear how it managed to get outside and into the pool as there are no cameras in the outdoor enclosure.
Zoo keepers think its mother, Melati, took it outside and a review has been launched as it was not expected she would take the cub outside so young.
A zoo spokeswoman said the mood has been low since the staff were told about the death.
Malcolm Fitzpatrick, zoo curator, told the Guardian: "We're heartbroken by what's happened. To go from the excitement of the birth to this in three weeks is just devastating.
"Melati can be a very nervous animal and we didn't want to risk putting her on edge by changing her surroundings or routines, in case she abandoned or attacked the cub. At the time we thought it was in the best interests of Melati and her cub to allow her continued access to the full enclosure as normal.
"We would do anything to turn back the clock, and nobody could be more upset about what's happened than the keepers who work with the tigers every day. They are devoted to those tigers and are distraught."
The cub was the first to be born to Melati and Jae Jae. The pair were introduced to the zoo's Tiger Territory enclosure in March to encourage breeding of the endangered species.
The cub's birth was captured on camera in the den following a six minute labour: "We couldn't have asked for a smoother birth," keeper Paul Kybett said at the time.