The UK's only female giant panda is no longer pregnant, Edinburgh Zoo has announced.
The zoo said there is no evidence Tian Tian has had a miscarriage, and that "late reabsorption of the foetus" could have taken place.
It said that all data gathered since the animal conceived in April suggested she was pregnant and likely carry to full term, but "sadly this did not happen".
The zoo said the panda is in great health, and is being monitored by experts.
Tian Tian was artificially inseminated on April 13 after she and her intended partner Yang Guang failed to mate naturally.
The zoo announced in August that she was thought to be pregnant and could give birth by the end of the month, however hopes of a cub faded when she passed her due date.
Hormone tests suggested that something might be amiss, though at the start of September the zoo said there was still a chance she could give birth to a live cub.
However, in a statement today the zoo confirmed that would not happen.
Iain Valentine, director of giant pandas for the Royal Zoological Society of Scotland, said: "Tian Tian's hormone levels have now returned to normal, so we can confirm that she is no longer pregnant.
"Panda reproduction and biology is complex; all data gathered since conception took place pointed to a pregnant panda likely to carry to full term, sadly this did not happen. There is no evidence she has had a miscarriage, so late reabsorption of the foetus could have occurred.
"Although Tian Tian has not successfully given birth, it is important for her individual biology as a female giant panda and for the future of giant panda conservation across the globe that we tried. We will also be reviewing all our data and procedures from this year and last.
"The team continue to monitor Tian Tian and she is in great health. The specialist team here and international colleagues will thoroughly review every aspect of how we care for her."
Tian Tian (Sweetie) and Yang Guang (Sunshine) are the first giant pandas to live in the UK for 17 years.
The animals, both aged 10, arrived on loan from China in December 2011 and will remain at Edinburgh Zoo for a decade.
Tian Tian was successfully inseminated last year but lost her cub at late term.
The attempt was the first artificial insemination procedure to take place on a giant panda in the UK.
She was again inseminated in April and the zoo confirmed in July that she had conceived but was not yet technically pregnant.
Experts said it would not be known for certain if she was pregnant until she gave birth.
The zoo said that the outdoor viewing area of Tian Tian and Yang Guang's enclosures will be open from today.