Auckland Zoo's 18-year-old Sumatran tiger has been put down after an examination showed the animal's age-related health problems were deteriorating.
Molek was put down yesterday after keepers and vets saw changes in her disposition, movement and appetite.
Vets will be performing a post mortem to find out what caused Molek's rapid decline.
The zoo said Molek - Malay for beautiful - was a grand old dame who lived a long and full life.
Senior vet An Pas said putting her to sleep was the right and kindest decision to make.
Molek was born in 2000 in Wellington before moving to Hamilton Zoo in 2001.
Auckland Zoo said it was a difficult time for staff and volunteers.
Team leader of carnivores Lauren Booth has been caring for Molek since the tiger moved to Auckland in 2006 and it was with some disbelief they were saying goodbye to "our beautiful tigress".
"She has left us with some exceptional memories from over the years which we will all cherish," she said. "One of my favourites is of the day we first found out she had given birth to three healthy cubs."
Two of the cubs now live at Tasmania Zoo, but the third, Berani, is still at Auckland Zoo.
Keepers hope that as Sumatran tigers are naturally solitary animals, Berani will adapt to his new situation.