Among those responding on Facebook - where she had more than three million followers - were people who work for animal charities which have benefited from the funds raised by Lil Bub's owner in his cat's name.
"On the morning of Sunday, December 1st 2019, we lost the purest, kindest and most magical living force on our planet", he wrote in a note. "BUB was cheerful and full of love laying in our bed with us Saturday night, but unexpectedly passed away peacefully in her sleep", he wrote.
In a tribute to Lil Bub posted Monday morning, Mike said she had helped the family raise more than $700,000 to help homeless animals across the state.
Her 2013 documentary "Lil BUB & Friends" won best online feature film at the Tribeca Film Festival.
Lil Bub was one of Instagram's most-recognizable furry stars, having developed a passionate following over her years in the spotlight. She had osteopetrosis (not osteoporosis), a condition that is rare in cats, which is why she didn't have any teeth and why her tongue stuck out (due to her lack of teeth and underdeveloped jaw).
"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", Bridavsky wrote, concluding the poignant obituary. She was a perma-kitten, which she meant she stayed kitten sized her entire life, and she had an "extreme case of dwarfism", which meant her limbs were disproportionately small relative to the rest of her body, so she had some trouble moving around.
Lil Bub was one of the original famous internet cats, rising to fame in 2012, one year after she was born, after she appeared on the front page of Reddit. She had to be bottle-fed, and had difficulty being adopted before her owner, Mike Bridavsky, took her in.
Eventually, Bub became so famous, her fans were willing to shell out up to $100 just to meet her at an event in Queens in 2016.
Millions of her fans were saddened to hear of Lil Bub's death.
She was originally picked up from a feral litter in IN in 2011, and was known for distinctive kittenish features that lasted well into her later years. She taught me everything that I know about unconditional love, she brought my wife Stacy and I together, she's the reason we have our attractive children Rosco and Lula, and she has been a constant source of warmth and love in our lives for the past 8 years. The next year, the cat dropped her own album Science and Magic, which according to AP, "rockets away from the shaky ground of meme culture and into a different space discovering the intersection between a sugar rush and solid songwriting". Bridavsky said his family was "devastated" by her passing.