King Harald V of Norway has died at the age of 89, the country’s Royal Court announced on Friday, August 28. Harald was Europe’s longest-serving reigning monarch.

“It is with deep sorrow that we announce the death of His Majesty King Harald. King Harald died peacefully at Oslo University Hospital Rikshospitalet on Friday, August 28, at 6:35 a.m.,” the Royal Court said on its website.

The day before, the Royal Court reported that the king was in “very serious” condition and that his health had deteriorated while he was receiving treatment at the hospital. His only son, 53-year-old Crown Prince Haakon, had already assumed the king’s duties during Harald’s hospitalization and is first in line to the Norwegian throne.

Harald V had been king since 1991, when he succeeded his father, King Olav V.