Lil Bub, a cat who rose to fame on the Internet, has died at age eight.

Lil Bub's owner, Mike Bridavsky, announced in an Instagram post Monday that Lil Bub died Sunday in her sleep.

Bridavsky shared a side-by-side photo of his first picture with Lil Bub as a kitten and the last photo he took with Lil Bub before her death. Lil Bub was known for her small stature and for her tongue hanging out.

"On the morning of Sunday, December 1st 2019 we lost the purest, kindest and most magical living force on our planet," Bridavsky wrote. "BUB was cheerful and full of laying in our bed with us Saturday night, but unexpectedly passed away peacefully in her sleep."

Bridavsky said Lil Bub was battling "a persistent and aggressive bone infection" prior to her death. Lil Bub was born with several genetic mutations, including feline dwarfism, and suffered from osteopetrosis.

Bridavsky adopted Lil Bub from a litter of feral cats in 2011. He credited Lil Bub with bringing him together with his wife, Stacy, with whom he has two children.

"It is impossible to put into words the profound effect that Bub has had on my life, on the lives of thousands of homeless pets, and on the lives of those of you that have cared for her as if she were your own family," Bridavsky wrote. "To say that our family is devastated would be an understatement."

"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. I am forever honored and humbled that you chose me as your caretaker," he added.

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The owners of other famous cats, including Klaus, Smoothie, Smush and Nala, were among those to voice their sympathies in the comments.

"Planet earth was a better place because of Bub's heart, determination, and generosity," Nala's owner wrote. "I truly believe that Bub will always and forever be with every heart she touched because she's capable of casting that kind of magic on people."

"We're so sorry for your loss," Smoothie's owner wrote. "Bub will always be in our hearts."

Lil Bub had over 2.3 million Instagram followers and 3 million likes on Facebook at the time of her death. She starred in the 2013 documentary Lil Bub & Friendz, which premiered at the Tribeca Film Festival.

Grumpy Cat, another Internet sensation, died at age seven in May.