A giant panda couple living in Vienna zoo naturally gave birth to a fourth baby pandas in ten years without any human intervention, it was reported Monday.

Schoenbrunn zoo announced that Yang Yang gave birth to a baby panda on Sunday afternoon. The pink cub is 10 cm tall and weighs about 100 gm. As the mother is spending all her time extremely close to her cub, the gender of the baby panda has not yet been identified.

"The nurses yesterday heard a squeak from the litter box. Yang Yang is an experienced mother and takes good care of her offspring. Nevertheless, one must remember mortality of giant pandas within the first year is around 40 percent," said zoo director Dagmar Schratter.

Yang Yang and father Long Hui are veritable superstars of the zoo. Schoenbrunn has already seen the birth of Fu Long in August 2007, his brother Fu Hu in August 2010 and Fu Bao in August 2013. The three panda cubs were also bred naturally.

The names of the three brothers mean lucky dragon, tiger and leopard.

The three panda brothers have all been sent back to China, according to a contract between China and Austria.