His owners announced via a Facebook post that he passed on in his sleep on the morning of January 18 at the ripe age of 12-years-old.
"Our family is heartbroken," the post said, "but we find comfort knowing that he is no longer in any pain or discomfort."
The Facebook page has over 16 million likes, and his Instagram -- formerly shared with his "best friend" Buddy -- has 546,000 followers. Buddy was also famous for being adorable and all things good in this world.
Buddy passed away in 2017, and Boo had had heart trouble since not long after his friend's death.
"I brought Boo home in the spring of 2006 and so started the greatest, most heartwarming friendship of all time," the post continued. "Shortly after Buddy died, Boo showed signs of heart issues. We think his heart literally broke when Buddy left us. He hung on and gave us over a year. But it looks like it was his time, and I’m sure it was a most joyous moment for them when they saw each other in heaven."
Boo, we hope you, Buddy, and Zsa Zsa are sharing a plate of spaghetti in dog heaven.