Crown Princess Mette-Marit of Norway shares two children with the future king Crown Prince Haakon - Princess Ingrid Alexandra, 20, and Prince Sverre Magnus, 18.
However, the queen-to-be also has a son, 27-year-old Marius, from her previous relationship with convicted felon Morten Borg, and he appears not to be living by the royal rulebook as his younger siblings are doing as heir and third-in-line to the throne.
Marius' arrest and drug use
The princess' eldest made headlines earlier this month as he was arrested for "psychologically and physically" attacking a woman in her 20s who was later revealed to be his girlfriend.
According to Se og Hør, Haakon's stepson spent more than 30 hours in police custody on Sunday 4 August following an "incident in an apartment" in Frogner, Oslo, and the woman was diagnosed with a concussion after being admitted to hospital.
In a statement via his lawyer, Marius said: "Last weekend something happened that should never have happened. I committed bodily harm and destroyed objects in an apartment in the intoxication of alcohol and cocaine after an argument."
He continued: "I have several mental disorders which mean that throughout my upbringing and adult life, I have had, and still have, challenges. I have struggled with substance abuse for a long time, something I have been in treatment for in the past. I will now resume this treatment and take it very seriously."
Marius added: "The drug use and my diagnoses do not excuse what happened in the apartment at Frogner on the night of Sunday last weekend. I want to be responsible for what I have done, and will explain myself truthfully to the police.
"For me, the most important thing is to say sorry to my girlfriend. She deserved neither what happened that night, nor the extreme pressure from both the Norwegian and foreign press afterwards. Being pursued by photographers and journalists at a time like this I know has been tough to stand in."
He continued: "I also want to apologise to my family. I know that my actions have greatly affected you. So to you my love, I'm sorry. This should never have happened and I take full responsibility for my actions."
Marius's life outside the royal rulebook
Marius is no stranger to defying the royal protocol that his siblings are subject to as the grandchildren of King Harald. In Norway, the 27-year-old has been referred to as the "black sheep" of the family as he sports tattoos and is a motorcycle mechanic.
He has accompanied his mother on royal engagements since her royal wedding in 2001. However, the royal family stated that he doesn't officially have a public role.
In fact, according to Se Og Hor, in 2016 Marius came under fire for selling luxury items online using the Royal Palace as his address despite living in Skaugum. Norwegian newspaper Dagbladet has since called Marius' circle of friends one of "rich heirs, reality celebrities and influencers", as well as "people convicted of dealing with cocaine and serious crime."
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Marius' father Morten Borg was in prison at the time of his birth for drug-related violent crimes. Mette-Marit was introduced to the father of her children by her former fiancé, John Ognby, who was also a convicted felon.