As Høiby prepared to celebrate his birthday on Friday, Mette-Marit published an open letter criticizing the press and telling them to stay away from her son.
"The last few years have been characterized by developments that I as a mother would naturally rather do without. Marius has been subjected to pressure from elements of the Norwegian press that I think is beneath them,” the Crown Princess wrote.
Mette-Marit that her family has essentially had media parked outside their house since Marius was a young boy.
“NRK Dagsrevyn [the broadcaster's evening news broadcast, ed.] followed us when we played in Frogner Park in the afternoon. Marius was 3 years old. Not even [tabloid] Se of Hør would think of doing that to a child today,” she wrote.
She added that Marius, as her son from a previous relationship, has always had a role that has been difficult to define in the public sphere.
"Marius was a symbol of the unusual choice we made when we were married, while at the same time he does not bear the public responsibilities of his siblings. He should not have a public role and is not a public person,” the letter states.
Kjell Arne Totland, an expert on the Norwegian royals, said Crown Princess Mette-Marit's open letter was essentially a declaration of love for her son.
"An unusually beautiful young man with an open mind. As a mother, I couldn't be prouder,” she wrote.
“I'm not so sure that the letter was solely intended as a rebuke of the press; I see that part as well, but first and foremost I think this is a declaration of love, a tribute from a mother to a son who is about to fly the coop,” Totland told TV2.
Next week, Høiby will begin studying for a degree in business administration in California. One of the reasons he is said to have chosen to study in the US is to escape the Norwegian press.
“That's why I am now choosing to request that the Norwegian media allow him to escape the attention that he doesn't want,” the Corwn Princess wrote.
The royals' communications manager Marianne Hagen did not want to go into specifics about what the princess was referring to when she wrote that “Marius has been subjected to pressure from elements of the Norwegian press that I think is beneath them.”
“It is a fact that coverage of Borg Høiby, in some parts of the press, has increased substantially,” Hagen told Dagbladet, which reported that the letter was sent out to express Høiby's desire to keep a low media profile.
The Norwegian Editors' Association responded to the letter by inviting Crown Princess Mette-Marit to a discussion.
“The criticism lacks specifics and is difficult to relate to. But we are happy to enter a dialogue with the crown princess and the royal family,” association spokesman Kjelling Nybø said.