Boo’s owners, who are from the United States, confirmed the canine celebrity passed away early on Jan. 19 at the age of 12.

“Our family is heartbroken but we find comfort knowing that he is no longer in any pain or discomfort,” they wrote.

His owners said Boo began having heart problems ever since his older friend Buddy, 14, died in 2017.

“Shortly after Buddy died Boo showed signs of heart issues. We think his heart literally broke when Buddy left us,” his owners wrote to fans on Facebook.

“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.”

The owner also shared to fans about how Boo had left behind a legacy of joy.

“Since starting Boo’s FB page, I’ve received so many notes over the years from people sharing stories of how Boo brightened their days and helped bring a little light to their lives during difficult times,” Boo’s owner said on Facebook after Boo’s death.

“That was really the purpose of all this … Boo brought joy to people all over the world.”

“Boo is the happiest dog I’ve ever met. He was so easy going … He made the manliest of men squeal with delight over his cuteness and made everyone laugh with his quirky, tail wagging personality.”

Boo first appeared in a photo book in 2011, called “Boo: The Life of the World’s Cutest Dog,” which featured his adorable self in multiple locations, with Buddy accompanying him in some.

The book has since been published in at least 10 languages—Portuguese, Finnish, French, German, Norwegian, Italian, Japanese, Korean, Turkish, and a Chinese-language edition sold in Taiwan. Boo has since appeared in another three photo books.

Boo rose to fame in late 2010, especially on the social media scene, and has 16.6 million likes on Facebook. Over the past decade, Boo featured on several TV shows, met with celebrities such as Seth Rogan, served as an ambassador for a U.S. airline, and in other partnerships. His contracts are reportedly worth about $1 million a year.