The court writes that King Haakon "has received with great sadness the news that Princess Astrid has passed away."
The princess died on Friday, but attended King Harald's funeral as recently as Wednesday.
"Thank you for being the best mother we could have. Throughout your life you were there for us, with love and wisdom, warmth and good humor. You were there for grandfather King Olav and uncle King Harald - present, loyal and dutiful," the princess's five children said in a statement.
King Haakon has decided that all public flags in Norway will fly at half-mast today and on the day of the funeral.
Prime Minister Jonas Gahr Støre remembers Princess Astrid with sadness and gratitude and thanks her for her contributions to Norway throughout her long life.
I remember Princess Astrid as a capable, dedicated and committed representative of the Royal House until the very end. My thoughts and condolences go out to her immediate family and to the Royal Family who have lost a dear family member.
Princess Astrid will be buried at state expense.
