Lil Bub, the adorable internet

Lil Bub, the Instagram-famous perma-kitten known for her bulging green eyes, droopy tongue, and delightful social media posts, has died.

On Monday, Lil Bub's human, Mike Bridavsky, shared the sad news on social media, along with a side-by-side photo composite featuring the first and last photo the two took together.

Per the post, Lil Bub was born in June 2011 and passed away on Sunday, Dec. 1. She was born with several genetic anomalies, including a rare bone condition called osteopetrosis, disproportionately small limbs, a lack of teeth, and an extra toe on all four paws. According to Bridavsky, before she died she was battling an "aggressive bone infection."

"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 in the post.

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He went on to say that "BUB" taught him everything he knows about unconditional love. "She brought my wife Stacy and I together, she's the reason we have our beautiful children Rosco and Lula, and she has been a constant source of warmth and love in our lives for the past 8 years. To say that our family is devastated would be an understatement."

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In 2012, Lil Bub made it to the front page of Reddit and captured internet users' hearts. After that spark of viral fame, other opportunities, including a feature on Good Morning America,soon presented themselves, and it wasn't long before BUB became one of the most famous cats online.

Lil Bub and her human, Mike Bridavsky Credit: annie colbert / mashable

Bridavsky also made sure to note that though Lil Bub was adorable, she was also quite the philanthropist and made a real impact in various causes.

"BUB has made a huge difference in the world of animal welfare, and in the lives of millions of people worldwide. She has literally saved thousands of lives (both pets and humans), she started the first national fund for special needs pets, she was the subject of groundbreaking genetic and biological research, she's helped raise over $700,000 for animals in need, and has spread a message of determination, positivity, and perseverance to people all over the world," Bridavsky wrote.

After news of Lil Bub's passing began to circulate, fans of the famous cat shared sweet tributes on social media.

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Bridavsky concluded the emotional Instagram post by writing, "Even though my heart is absolutely crushed by her graceful departure from planet Earth, I know that her sprit, magic, and overwhelming energy are still with us, reminding us every day to be better."

UPDATE: Dec. 2, 2019, 1:27 p.m. EST Updated with additional information about Lil Bub.