He was 12 years old. Poor little guy. Very saddening too.
https://mashable.com/article/boo-intern ... LzZNc9Isqk
Though Boo's humans are "heartbroken," they explained they're hopeful that Boo will soon be reunited with his best friend Buddy, who died in Sept. 2017.
"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."
"We find comfort knowing that he is no longer in any pain or discomfort. We know that Buddy was the first to greet him on the other side of that rainbow bridge, and this is likely the most excited either of them have been in a long time," Boo's owners explained.