Tuan Tuan and his breeding mate Yuan Yuan were given to Taiwan by Beijing at a time when relations between the two neighbours were more cordial.
In a nod to the Chinese Communist Party’s goal of one day taking Taiwan, their names combined mean “reunion” or “unity”.
The couple became huge stars in Taiwan and Yuan Yuan has since given birth to two female cubs.
“He (Tuan Tuan) was small and so cute when he first got here,” said Heng Ling-lin, who brought her children to Taipei Zoo to sign get-well notes.
“He was like everybody’s baby,” she told AFP.
“It breaks my heart now to see him like this.”
“PANDA DIPLOMACY”
China only loans pandas to foreign zoos which must usually return any offspring within a few years of their birth to join the country’s breeding programme.
But Taiwan was granted an exception as part of a brief charm offensive China launched in the late 2000s and was fully gifted both Tuan Tuan and Yuan Yuan and any offspring they had.
Vets first noticed Tuan Tuan, 18, was ill in August when he began suffering seizures and appeared increasingly unsteady and lethargic.
Subsequent scans showed he had a brain-lesion and he was placed on anti-seizure medication.
Earlier this week Taipei Zoo said they suspected Tuan Tuan had a brain tumour and he was moved into palliative care.