Norway’s King Harald V was admitted to the main hospital in Oslo to undergo an operation that would replace a heart valve, the palace announced on Thursday.

“This intervention is necessary to improve the king’s breathing," the monarch’s doctor, Bjoern Bendz, said in a palace statement. "This type of operation is performed several hundred times a year at Rikshospitalet."

The aging monarch was hospitalized last month with breathing difficulties. However, doctors ruled out COVID-19 as the cause.

The royal household in Oslo revealed the king is on sick leave until further notice. His son and heir to the throne, Crown Prince Haakon, has stepped in and taken over his father’s duties.

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The palace said the operation will not be open-heart surgery. The king will be awake, and the operation will be performed via the groin with local anesthesia. It is scheduled for Friday at the hospital’s Cardiovascular and Lung Clinic.

Norway's King Harald V was admitted to the main hospital in Oslo to undergo an operation that would replace a heart valve, the palace announced on Thursday.

Norway's King Harald V was admitted to the main hospital in Oslo to undergo an operation that would replace a heart valve, the palace announced on Thursday. (Photo by Marcelo Hernandez/Getty Images)

In 2005, Harald's aortic valve was replaced by an artificial heart valve. The royal household noted these types of valves have a lifespan of between 10 and 15 years. Therefore, it is “not uncommon” for such interventions to have to be repeated.

Harald ascended the throne upon the death of his father, 87-year-old King Olav, in 1991.

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The country’s first native-born king since the 14th century, Harald married a commoner, now Queen Sonja, as a prince in 1968. The couple shares two children. Harald also won hearts in his country by leading the mourning in 2011 for the victims of mass killer Anders Behring Breivik.

The Associated Press contributed to this report.