The first tiger cub to be born at London Zoo for 17 years has died.
Keepers at the zoo are "very distraught" after the cub was discovered on the edge of the pool inside the tigers' enclosure, a ZSL London Zoo spokeswoman said.
"The keepers are naturally very distraught. They work very closely with the tigers, so it is incredibly sad news for them," she said.
Five-year-old Sumatran tiger Melati gave birth to the cub two weeks ago , with the event captured on hidden cameras in the den.
Keepers raised the alarm in the early hours of Saturday morning after they noticed that they could not see the cub on the den cameras.
The zoo spokeswoman said a post-mortem examination conducted on Sunday confirmed the cub had drowned.
It is thought that Melati carried the cub outside but keepers are unclear as to how the cub got into the pool as there are no cameras in the wider enclosure.
Keepers are reviewing the situation as it was not envisaged that the mother would take the cub outside so early.
Curator Malcolm Fitzpatrick said: "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."
Melati's pregnancy lasted around 105 days and was kept secret by zookeepers, who maintained a careful watch on the first-time mother through hidden cameras so they would not disturb her.
The cub, which was too young to be sexed or named, was born six months after the opening of the new "tiger territory" at London Zoo, designed to encourage breeding of the critically-endangered sub-species of tiger.
The cub is the grandchild of the zoo's last tiger cub, Hari, the father of Melati.
The cub's father is five-year-old Jae Jae, which had been playing no part in taking care of the new arrival.