The social media sensation's owners confirmed on Facebook that the dog had passed away in his sleep, going "over the rainbow bridge" to join his best friend, Buddy.
Boo had started experiencing heart problems when his best friend died in 2017.
Boo and Buddy's owners
"I brought Boo home in the spring of 2006 and so started the greatest, most heartwarming friendship of all time. 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 love you with all our hearts and will miss you until the day we meet again. Have fun running around with Buddy and creating adorable mischief wherever you guys go."
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Boo and Buddy[/caption]
The post went on to describe how people had sent "so many notes over the years", sharing how Boo had "
"Over the years Boo met some super cool people, a lot of crazy talented people, but most of all so many kind people...friends who gave him endless love, people who prioritized his comfort over getting that perfect picture, partners who understood that Buddy ALWAYS had to be included."
The Facebook post ended with a thank you to the vets who had taken care of Buddy and Boo, and a thank you to everyone for "following along on their silly adventures over the past 10 years."