Boo the pomeranian, who captured hearts on the Internet after he was named the world's cutest dog, has died from "heartbreak", his owners said on Facebook on Saturday (Jan 19).
The owners of the 12-year-old dog, who call themselves Boo's humans, said that he had showed signs of heart issues shortly after his best friend and fellow pomeranian Buddy died about a year ago.
They wrote: "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."
Announcing that Boo had died in his sleep on Saturday morning, his owners added that they are heartbroken, but find comfort in knowing that their dog is no longer in any pain or discomfort.
Boo's friendship with Buddy blossomed in 2006 when he joined the family, who are based in San Francisco.
In 2010, Boo shot to fame on the Internet, after singer Ke$ha and reality TV star Khloe Kardashian tweeted about the pint-sized pup.
American media had dubbed him the world's cutest dog and his following on social media grew steadily over the past decade to more than 16 million.
He even has three picture books to his name - Boo: The Life Of The World's Cutest Dog (2011); Boo: Little Dog In The Big City (2012); and Boo ABC: A To Z With The World's Cutest Dog (2013).
Photos of Boo and Buddy, which are posted several times a week, often show the dogs going about their daily lives at home or on excursions around San Francisco.
In the post, Boo's owners said that since starting the Facebook page for Boo, they have received many notes from people sharing stories of how Boo has brightened up their day, especially during difficult times.
"Boo brought joy to people all over the world," they wrote, adding that he was the "happiest dog I've ever met".
"He was so easygoing that we never had to bother with training. He made the manliest of men squeal with delight over his cuteness and made everyone laugh with his quirky, tail wagging personality," they said.
Despite his growing fame, Boo was always the happiest by Buddy's side.
"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 prioritised his comfort over getting that perfect picture, partners who understood that Buddy ALWAYS had to be included," they wrote.
The owners also thanked the staff members at Adobe Animal Hospital and Sage Veterinary Centres for their care and dedication in caring for Buddy and Boo.
"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," they added.
Thousands of Boo's fans from across the world have left comments in Saturday's post, expressing their sadness over his death.
Within five hours after it was posted, the post received at least 145,000 likes and around 23,000 comments.
Facebook user Jackie Wood wrote: "I loved following Boo's adventures. He was a super cute little guy. I would never want Boo, Buddy or any animal to suffer, but this breaks my heart. Run free with Buddy over the bridge, little Boo."