Rostov-on-Don (Russia) - His name is fit for a king, and he's being treated like one: Tsar the liger cub, born from an extremely rare lion-tiger romance, is proving a hit for a travelling Russian zoo.
Stretched out in the zoo director's van, the stripy Tsar -- whose name is a throwback to the Russian emperors of centuries past -- impatiently awaits his milk bottle.
"We don't leave him in a cage -- it's too cold outside," said zoo chief Erik Airapetyan. "We keep him here with us -- he even sleeps in our bed."
With the tawny fur of a lion cub but covered in black stripes, Tsar was born on November 11 while the zoo was on tour in southern Russia's Rostov-on-Don region.
Airapetyan and colleagues are feeding him with goat's milk, and so far, he drinks about a litre (two pints) a day.
His mother Princess, the zoo's only tigress, had a difficult birth and has been unable to suckle him. She has given birth to a total of three liger cubs, but only Tsar has survived, according to Airapetyan.
"Hybrids like this are extremely rare -- and generally they are weaker than lion cubs or ordinary young tigers," explained Dmitry Miloserdov, a researcher at Moscow's Darwin Museum of natural history.
"But if you take good care of them, they can grow up and live a long time," he told AFP, adding however that male ligers are born sterile.
Mindful that Tsar's survival is against the odds, the zoo is catering to his every whim: he has an unlimited milk supply, sleeps 16 hours a day, and plays whenever he wants.
"We're all taking care of him -- we're very proud of our little treasure. He's unique, our stripy lion," Airapetyan smiled.
Neither Princess or Tsar's father, Caesar the lion, have access to the cub for the moment.
At two and a half months old and weighing five kilograms (11 pounds), he is "still too small and fragile" to meet his parents, said Airapetyan.
Princess and Caesar have occupied neighbouring cages for years and "are used to one another", according to the zoo director.
Every time she is in heat, the zoo faces a tricky dilemma: offer Caesar as a suitor, or deal with the wrath of a sexually frustrated Princess.
"So we dared to half-open the dividing wall between the cages," Airapetyan recalled. "Then seeing that everything was going well, we took to risk of leaving them face to face."
When it became clear Princess was pregnant, "everyone was so happy", he said.
"It's so rare, a liger! Right now there are only about 20 in the world," he added, grinning from ear to ear.
Ligers, like tigons -- cubs born to a lioness and a male tiger -- can only be born in captivity, Miloserdov noted, not least because almost all wild lions live in sub-Saharan Africa, and tigers in the jungles of Asia.
"They only cross over in India -- but even there, their cycles of being in heat are very different," Miloserdov said.
For now, Tsar is only the size of a large house cat and "he often sleeps in my arms," said Airapetyan.
"But when our little king grows up, he will surely be heavier than his parents," he predicted.
Ligers can weigh more than 400 kilograms (63 stone), compared to a maximum weight of about 300 for a tiger and 250 for a lion.
Hercules the liger, who lives at a wildlife reserve in United States, is the world's largest living cat, at 418 kilograms and 3.33 metres (10 feet 11 inches) long, according to the Guinness Book of World Records.