The cub died due to a liver inflammation just four months after his birth, Tierpark director Andreas Knieriem said on Tuesday.
“We're stunned, very sad and depressed. It's unbelievable how quickly we fell in love with this little bear,” he said.
Fritz was born to seven-year-old female Tonja and five-year-old Wolodja, and was the first polar bear cub born in Berlin's Tierpark in 22 years.
Since his birth on November 3rd, Fritz hadn't yet ventured outside of the enclosure where his mother had cared for him. In video released by the zoo in December, Fritz could be seen trying to take his first steps.
At the weekend zookeepers first noticed that something was wrong with the cub. He was lethargic and by Monday seemed to have little energy left at all.
After a crisis meeting involving veterinarians and zookeepers, the cub was separated from his mother and taken for tests at a nearby clinic. The examination brought up little concrete, but the little cub was given a special antibiotic due to a poor liver function reading.
As they day wore on though, his condition worsened. By Monday evening his breathing had become uneven. Emergency procedures did nothing to improve the situation, and at around 8pm the frail cub stopped breathing and died.
This isn't the first time that the premature death of polar bear has left Berlin animal lovers in mourning.
In 2011 the beloved polar bear Knut died at the age of four at the Zoologischer Garten.
Knut had become an international celebrity, even appearing on the cover of Vanity Fair magazine, after his mother rejected him and he was raised by a zookeeper.
An autopsy was being carried out on Fritz on Tuesday morning.
"Fritz did not make it," said top-selling Bild daily on its online homepage and in a tweet.
"So sad to hear that Berlin's baby polar bear Fritz passed away," tweeted English Choir Berlin.
The chancellery joined in the mourning, with Angela Merkel's chief of staff Peter Altmaier attaching Bild's tweet and adding: "Anyone who remembers little Knut is sad. But above all, we must protect polar bears in nature!"