The Pomeranian Boo and his buddy Buddy, who died last year, became sensations on the Internet when their American owners began sharing photos of their lovable antics.
"Shortly after Buddy's death, Boo showed signs of heart problems, and we think his heart literally broke when Buddy left us," the owners wrote. "He stayed and gave us more than a year, but it seems it was his time, and I'm sure it was a very happy moment for them when they saw each other in heaven.
"Our family is disconsolate, but we feel comfortable knowing that they no longer feel any pain or discomfort," they added, noting that Boo "brought joy to people around the world."
The announcement was received with surprise by Boo fans, several of whom said they were crying for the news.
Venus The Two Face Cat, a chimera cat with more than a million Facebook fans, "wrote:" "He is a true legend and we have enjoyed watching him for the last 6.5 years."
In addition to his presence on social media, Boo was named in 2012 as the official pet liaison for Virgin America. He also had a book contract, which appeared in photo albums that included "Boo: The Life of the Cutest Dog in the World," published in 2011.
A previous rumor that Boo had died was denied by Anderson Cooper of CNN in 2012.