A dog once named the world’s cutest has died of a “broken heart.”

Boo the Pomeranian was a social media sensation with 16 million followers on Facebook.

The adorable pup’s U.S. owners said in a Facebook post that after the dog’s friend Buddy died, Boo showed signs of heart issues.

Boo and its best dog pal Buddy had lived together for 11 years - before Buddy passed away in September 2017 at the age of 14, according to the owners.

“We think his heart literally broke when Buddy left us,” they said in a Facebook post.

“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 passed away in his sleep early on Friday morning, his devastated owners said.

As well as releasing a book, Boo met with celebrities, including Canadian comedian Seth Rogen, and appeared on several TV shows in the U.S.

“He was so easy going that we never had to bother with training,” his owners said.

“He made the manliest of men squeal with delight over his cuteness and made everyone laugh with his quirky, tail wagging personality.”