The Norwegian royal palace issued an update on Crown Princess Mette-Marit's health on Thursday.
The Norwegian royal, 51, was diagnosed in 2018 with pulmonary fibrosis, a chronic lung condition that causes the lung tissue to become damaged.
In recent years, she has had to take several periods of sick leave from her public duties and reduce her workload.
A statement from the palace on Thursday confirmed that Mette-Marit's illness unfortunately has progressed.
It read: "The Crown Princess has daily symptoms and ailments that affect her ability to perform her duties. The Crown Princess needs more rest, and her daily routine changes more quickly than before. This means that changes to her official schedule may occur more frequently, and at shorter notice than we are used to.
"The Crown Princess has a strong desire to continue working, and therefore we will organize her official program in the future in the best possible way so that her health and work can be combined."
Mette-Marit was last seen publicly on Wednesday as she visited a children's ward at Ulleval Hospital.
© BERG-RUSTEN/EPA-EFE/ShutterstockWhen her diagnosis was first confirmed in 2018, Mette-Marit opened up about her condition, sharing: "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."
After restricting her royal duties, she told 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."
Mette-Marit married Crown Prince Haakon – heir to the Norwegian throne – in 2001.
She has a 28-year-old son, Marius Borg Høiby, from a previous relationship. Marius is currently under investigation for a number of alleged serious offences.
© GettyThe Crown Prince and Crown Princess are also parents to Princess Ingrid Alexandra, 21, and Prince Sverre Magnus, 19.
