In a statement on Twitter, Grumpy's owners revealed that despite efforts to save her, she encountered complications from a urinary tract infection. And, the illness became 'too tough for her to overcome.'
The famous and adorable cat, who was only seven, sadly died at home in the arms of her mommy, Tabatha.
The full statement reads: "We are unimaginably heartbroken to announce the loss of our beloved Grumpy Cat.
"Despite care from top professionals, as well as from her very loving family, Grumpy encountered complications from a recent urinary tract infection.
"Besides being our baby and a cherished member of the family, Grumpy Cat had helped millions of people smile all around the world – even when times were tough.
"Her spirit will continue to live on through her fans everywhere."
The cat, who got her name from her seemingly grumpy facial expression, won over the hearts of everyone over her Instagram account.
Grumpy Cat has 2.4 million followers on Instagram. She became famous in 2012 after owner Bryan posted a photo of her on Reddit.
Thanks to her unique look, caused by an underbite and feline dwarfism, she became internet famous. The cat earned at least $1 million.
People are, predictably, completely gutted, with tributes pouring in for the gorgeous feline on social media.