Lil BUB, the beloved viral internet cat known for her perennially stuck out tongue and massive eyes, has died, her owner announced in an emotional Instagram post Monday. She was 8 years old.

"Dearest BUB, I will never forget your generosity, your limitless supply of love, or your uncanny ability to bring so much magic and joy to the world," owner Mike Bridavsky wrote on her official Instagram page. "I am forever honored and humbled that you chose me as your caretaker. Please visit all of us in our dreams."

Bridavsky said the famous feline was "cheerful and full of love laying in our bed with us Saturday night," but passed away "unexpectedly" in her sleep by Sunday morning. The cat had many health issues and was battling a bone infection, which Bridavsky had openly posted about on social media. But he said she was not expected to pass away "so soon."

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"I truly believe that she willingly made the decision to leave her failing body so that our family would not have to make that difficult decision ourselves," Bridavsky added in the caption, which accompanied his first and final photos with her.

In 2011, Lil BUB was discovered as a kitten in a rural Indiana toolshed as the runt of a feral litter of cats. She was born with "a multitude of genetic anomalies," according to her website.

The feline was a "perma-kitten," meaning she retained her kitten-like features and remained "kitten sized" for her entire life. She also had an "extreme case of dwarfism," so her limbs were disproportionately small in relation to the rest of her body. Her lower jaw was much shorter than her upper jaw, and her teeth never came in, which lead to her signature hanging tongue.

She first rose to fame when Bridavsky posted about her on Tumblr, CNET reported. At the time of her death she had over 2.4 million Instagram followers. Lil BUB has been featured on various types of merchandise and stuffed toys, appeared on television many times, and even has her own book.

The famous pet and her owner also regularly used her platform to advocate for other animals. Her national fund for special needs pets, Lil Bub's Big Fund for the ASPCA, has helped raise hundreds of thousands of dollars for animals in need since 2014, according to her website. She was also "the subject of groundbreaking genetic and biological research," according to Bridavsky's post.

This year has not been a good one for internet cats. Grumpy Cat, the world-famous feline whose signature frown is used in memes everywhere, died at age 7 in May. Despite care from top professionals and loved ones, her family said she died following complications with a recent urinary tract infection.