Brown bear Amu was the oldest of the four bears who undertook the 5,400 mile trip to the UK earlier this month.
But bosses at the Branton-based visitor attraction at had to make the heartbreaking decision to put the 27-year-old animal to sleep after medical checks.
A statement on the park's website said: 'We regret to announce the death of Amu.
'An extensive veterinary examination once he arrived in the UK revealed the full extent of several chronic degenerative disease processes including arthritis and heart disease, which were unfortunately more severe than first thought.Â
'Vets and YWP staff tried a wide variety of treatments, constantly monitoring his condition hoping to see improvement.
'Sadly, after weeks of trying to improve his health, the vets and YWP decided that on welfare grounds, there was no choice but to put him to sleep. This was obviously a deeply difficult decision and very hard for the staff who had been caring for him since his arrival.
'We would like to thank everyone, who helped bring the bears to YWP. We are pleased to report that the other three are in good health and thriving in their new surroundings.'
Amu arrived in the UK after a huge two month logistics operation to ensure the animals were transported safely.
Riku, Kai, Hanako andÂ AmuÂ were previously housed as part of an exhibit in outdated cages at the Ainu Cultural Museum on Hokkaido, the northernmost ofÂ Japan's islands and urgently needed new facilities. Unfortunately, there was no capacity inÂ JapaneseÂ zoos to take them, so YWP stepped in.Â
YWP and local experts spent nearly seven hoursÂ moving the fourÂ bearsÂ from the bleak cramped cages into specially constructed transport crates ready for their journey from Tokyo to London's Heathrow before being transported by road to Doncaster.
The Ussuri BrownÂ BearÂ is on the IUCN Red List of Threatened Species due to their vulnerability to habitat loss, illegal hunting for body parts and skins. There are estimated to be around 10,000 inÂ Japan. The Ussuri BrownÂ BearsÂ are also known as the Black Grizzly, can weigh up to 550Kg and live up to 35 years.