Grumpy Cat
Grumpy Cat has amassed a mutli-million dollar fortune after becoming an internet sensation. AFP / Getty Images

She is the most famous feline in the world and the grumpiest by far.

And even the news that she is now worth £64 million wasn't enough to put a smile on Grumpy Cat's face.

The cat, whose real name is Tardar Sauce, first shot to fame two years ago, when a video posted on YouTube by her owner, went viral with 15.7 million views.

Her perpetually frowning face has spawned a series of lucrative business ventures including a best-selling series of books, a Hollywood movie, toys, calendars, mugs and T-shirts. She has acquired 521,000 followers on Instagram and 255,000 on Twitter.

What she's achieved in such a short time is unimaginable and absolutely mind-blowing.
- Tabatha Bundesen, Grumpy Cat's owner

Her first book, titled Grumpy Cat: A Grumpy Book, was a guide to attaining 'true grumpiness.' The follow-up, The Grumpy Guide To Life: Observations By Grumpy Cat, advises that "It's always good to have a partner in crime - you need someone to blame when people start asking questions."

She represents Friskies cat food and has even leant her image to a brand of iced coffee, called Grumppuccino.

Grumpy Cat made her Hollywood debut with Grumpy Cat's Worst Christmas Ever, voiced by Parks and Recreation star Aubrey Plaza, which became the most tweeted about film on its release date making millions at the box office.

As a result of all her commercial enterprises, the moggy's income now rivals that of Hollywood stars Nicole Kidman, Cameron Diaz and Matthew McConaughey.

Owner Tabatha Bundesen from Morristown, Arizona, said the two-year-old cat has changed her life.

She told The Express: "What she's achieved in such a short time is unimaginable and absolutely mind-blowing. I was able to quit my job as a waitress within days of her first appearance on social media and the phone simply hasn't stopped ringing since."

Grumpy Cat's permanently dour expression is the result of an underbite and dwarfism.