Once he was born, the tiny infant was small enough to be held in the palm of an adult's hand, and weighed just slightly more than a quarter of a kilogram.
Now, thanks to staff at the hospital, he weighs more than 7lbs - a perfectly healthy weight for a newborn baby - and is as healthy as can be. He's also feeding properly, and that means that he can go home with his mother.
The baby boy was born and spent the first few months of his life in Keio University Hospital in Tokyo, Japan. His thankful mum said: "I can only say I'm happy that he has grown this big because honestly, I wasn't sure he could survive."
The hospital have since confirmed that they think he is probably the smallest boy (at birth) to be safely discharged in good health afterwards.
One of the doctors that treated the young boy, Dr. Takeshi Arimitsu said that he wanted to offer the encouragement that 'there is a possibility that babies will be able to leave the hospital in good health even though they are born small'.
In case you were wondering, the previous record was held by a child born in Germany in 2009. The baby boy weighed only 274 grams. The Japanese boy was only 268 grams, which seems to be the lightest on record.
In confirming their assertion that this kid is the smallest ever born to return safely home with his parents, they cited a register from the University of Iowa that compiles a list of the tiniest babies born.
You'll notice that this record that they claim is only for the boys. That's because there have been even smaller girls born that have been successfully brought to good health.
In 2015, a baby girl was born in Germany that weighed just 252 grams. However, this story is noteworthy, as the survival rate for tiny babies is much lower in boys than in girls.
The important thing is that this little fighter is alive and well, and can now return home with his loving family, just two weeks after their original due date. Our best wishes go to the little one and his family, and a huge shout out to the staff at the hospital for working miracles!