Crown Princess Mette-Marit has been placed on sick leave for a week, the Norway palace has confirmed.
It comes just weeks after the future Queen Consort, 51, started treatment for pulmonary fibrosis, a chronic lung condition that causes the lung tissue to become damaged.
A statement from the royal court released on Wednesday read: "Due to side effects of the medicines the Crown Princess must take for her chronic lung disease, she is on sick leave, initially for a week. Program items during the period will be cancelled or postponed."
Mette-Marit's diagnosis was first confirmed in October 2018, with the royal sharing a the time: "For a number of years, I have had health challenges on a regular basis, and now we know more about what these are.
"Although such a diagnosis will limit my life at times, I'm glad that the disease has been discovered so early. My goal is still to work and participate in the official programme as much as possible."
Since her diagnosis, the Crown Princess has had to restrict her public duties, telling TV network NRK in 2019: "I am exhausted faster than before, so today I have to take more care of myself than I did before."
The Crown Princess Mette-Marit was last seen publicly on Monday as she travelled to Berlin with her husband, Crown Prince Haakon, to mark the 25th anniversary of the Nordic countries' joint embassy facility in Berlin.
The Norwegian royals were joined by Denmark's King Frederik and Queen Mary, and Sweden's Crown Princess Victoria and Prince Daniel at a joint ceremony outside the embassy, as well as a formal dinner at the Bellevue presidential palace.
Mette-Marit and Haakon are parents to Princess Ingrid Alexandra, 20, and Prince Sverre Magnus. The Crown Princess also has an older son from a previous relationship – Marius Borg Høiby.
It's been a challenging time for the family of late as 27-year-old Marius admitted to assaulting his 'girlfriend' following his arrest in August.