Ten year-old Lennu passed away on Friday from complications related to brain cancer, the president's office tweeted on Saturday.
"If it were up to how much we loved you, you would have lived forever," Jenni Haukio tweeted.
Over the years, Lennu was known for stealing the show at formal functions. His distinctive grin attracted attention across social media, with fans including Tonight Show host Jimmy Fallon as well as the New York Times.
At the height of Lennu's fame, Helsinki-based Café Esplanad even created a dog-faced pastry bearing his name.
In recent years, Lennu stayed out of the limelight.
A debate in Finland about the dark side of dog breeding prompted the country’s first family to relegate their pet terrier to the sidelines, according to President Sauli Niinistö.
In 2020, a report by the Natural Resources Institute (Luke), the Ministry of Agriculture and the Finnish Food Authority found that brachycephalic dogs like Lennu (dogs with flat faces or short snouts) are prone to hereditary defects and diseases that impair their quality of life and cause suffering and considerable harm.
"When we got Lennu, we had no idea about the problems related to the breeding of dogs with short snouts," the president said at the time.