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.

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."

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.

Image: 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.

Really, truly devastated by this. All of the good that Lil BUB and her owner Mike Bridavsky have done for special needs animals has been nothing short of inspiring.



Leave it to the littlest cat show us people can be better. https://t.co/2DWWuCEkx1 — Christian Ryan (@ChristianRyanNS) December 2, 2019

#LilBub has died and nothing else matters today.



Rest well, sweet kitten. You were a good cat and I love you. pic.twitter.com/uKGOxkMLny — Jill Hopkins (@Jillhopkins) December 2, 2019

I am sad to hear that Lil BUB passed away. She was a great cat who inspired real joy, and I'll fire up her yule log videos every year.



It also occurs to me that a generation of internet-famous pets will soon be departing us in droves, and I'm not sure I'm ready for it. pic.twitter.com/OY4WR70wcj — Alan Zilberman (@alanzilberman) December 2, 2019

Lil Bub has left this plane of existence.



Thank you for bringing so much joy into this world, you sweet, goofy creature.



In our hearts always. pic.twitter.com/rbHbAoeKeR — Kyle Gaddo (@kylegaddo) December 2, 2019

you know what lil bub did that was really fucking cool? reminded us all that we’re a bunch of beautiful freaks and how special it is to be a beautiful freak. — dedicated to JVs who came feet first (@JVeezus) December 2, 2019

I'M CRYING !!!!!!!!!!!!!!!!! 💕 What a sweet, beautiful, persevering cat & family. They raised so much money for homeless pets and changed the lives of so many animals & people. She struggled with medical issues her whole live but they made the best of it 💕😭 https://t.co/ClIhgWzZ6a — [🔴 LIVE] ♫ ° 𝑅𝑒𝓏𝓏𝒶 ° ♫ (@RezzaTV) December 2, 2019

You were a quality, cute, alienesque cat Lil Bub.

Thank you for your service to all of us humans. pic.twitter.com/obqtqLz8J1 — 🤴🏾🤴🏾🤴🏾Magi! at the Manger🌠 (@katynotie) December 2, 2019

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.