Nicknamed "Hvaldimir" in a pun on the Norwegian word for whale, hval, and its purported ties to Moscow, the beluga first appeared off the coast in Norway's far-northern Finnmark region in 2019.
At the time, Norwegian marine biologists removed an attached man-made harness with a mount suited for an action camera and the words "Equipment St. Petersburg" printed on the plastic clasps.
Norwegian officials said Hvaldimir may have escaped an enclosure and may have been trained by the Russian navy as he appeared to be accustomed to humans.
Moscow has never issued any official reaction to speculation that he could be a "Russian spy".
On Saturday, the beluga's lifeless body was discovered off the southwest coast at Risavika by Marine Mind, an organisation that has tracked his movements for years.
"I found Hvaldi dead when I was scouting for him yesterday like usual," Marine Mind's founder Sebastian Strand told AFP.
"We had confirmation of him being alive little more than 24 hours before finding him floating motionlessly," he added.
Fredrik Skarbovik, maritime coordinator at the port of Stavanger, confirmed the beluga's death to the VG tabloid newspaper.
Strand said the cause of the whale's demise was unknown and no visible injuries were found during an initial inspection of Hvaldimir's body.
"We've managed to retrieve his remains and put him in a cooled area, in preparation for a necropsy by the veterinary institute that can help determine what really happened to him," Strand added.
With an estimated age of around 14 or 15, Hvaldimir was relatively young for a Beluga whale, which can live to between 40 and 60 years of age.
Beluga whales can reach a size of six metres (20 feet) and generally tend to inhabit the icy waters around Greenland, northern Norway and Russia.
Those include the Barents Sea, a geopolitically important area where Western and Russian submarine movements are monitored.
It is also the gateway to the Northern Route that shortens maritime journeys between the Atlantic and Pacific oceans.
