Norway's 83-year-old King Harald V was admitted to the main hospital in Oslo on Friday with breathing difficulties, the Norwegian palace said. It added that he tested negative for COVID-19.
The palace said his son, Crown Prince Haakon, has stepped in and taken over his father's duties, including a scheduled meeting with the Norwegian government.
"The king is now being examined. COVID-19 is already excluded," the palace said in a later statement.
Harald ascended the throne upon the death of his father, King Olav, on Jan. 17, 1991.
The country's first native-born king since the 14th century, he married a commoner as a prince and won hearts in his egalitarian country by leading the mourning in 2011 for the victims of mass killer Anders Behring Breivik.
In 2016, a speech by Harald in support of gay rights and diversity attracted widespread international attention. "Norwegians are girls who love girls, boys who love boys, and girls and boys who love each other," he said.
The speech was shared tens of thousands of times on social media.
Earlier this year, Harald was briefly admitted to Rikshospitalet, the capital's university hospital, after experiencing dizziness. No serious illness was found, but the monarch was on sick leave for two weeks.