Grumpy Cat - real name Tardar Sauce - shot to fame in 2012 in a YouTube video that received 15.7 million views, and went on to amass a $100M fortune for her former-waitress owner Tabatha Bundesen.
But her family from Morristown, Arizona, took to Instagram this morning to announce the news that she'd died on Tuesday from a urinary tract infection, saying: 'Some days are grumpier than others'.
The internet sensation was born with feline dwarfism and an underbite, which caused her famous expression.
However her condition also brought with it a number of health complications, including infections, which experts say drastically reduced her lifespan.
Heartbroken fans have rushed to pay tribute to the much-loved pet online, with one summing up the feelings of many by writing: 'We are all a bit of you.'