The cat's image was hot property: a year ago, a California jury awarded Bundesen's company, Grumpy Cat Limited, damages of $710,001 in a lawsuit against a beverage company that had created an unauthorized line of "Grumpy Cat Roasted Coffee" and which was selling Grumppuccino tee-shirts without sharing profits.
Grumpy Cat, hero of a million memes, has gone to the great Twitter thread in the sky.
Revealing the news on social media, her family said that they were "unimaginably heartbroken to announce the loss of [their] beloved" pet.
All here Daily Star online would like to express our condolences to the owners friends and fans of Grumpy Cat, the only GC that really matters. The glum feline made appearances on American Idol, The Bachelorette and WWE's Monday Night Raw.
According to his owners, the cat from Arizona, whose real name was Tardar Sauce, "helped millions of people smile".
Owner Tabatha Bundesen founded Grumpy Cat Ltd. and created a website that included an online shop featuring 884 items, including T-shirts and mugs with the cat's picture.
Before long, her disgruntled expression - which is said to be a side effect of both her underbite and feline dwarfism - had been seen by over one million people, with many claiming that the miserable-looking moggy had been Photoshopped. She became an internet sensation in 2012 when images of her downturned mouth and unimpressed expression emerged on Reddit.
She has 2.4million followers on Instagram, travels first class and stays at the very best hotels.
"Some days are grumpier than others", it began. She's done television commercials for Honey Nut Cheerios and took photos with hundreds of fans at South by Southwest.