Although he has grown up as Crown Prince Haakon’s stepson, Marius Borg Høiby is not a member of the royal family or a public figure.
However, the first count of rape is alleged to have taken place in his parents’ basement on their Skaugum estate outside Oslo.
As the trial began at Oslo district court on Tuesday, the palace came under increasing pressure to explain his mother’s three-year exchange of messages with the late sex-offender Jeffrey Epstein between 2011 and 2014.
Crown Princess Mette-Marit has already admitted to “poor judgement”, after details emerged of a four-day stay at his home in Palm Beach, Miami. But the palace has said little more as further revelations have emerged.
No photos were allowed as her son entered courtroom 250 at Oslo district court at the start of a seven-week trial.
Wearing thick-rimmed glasses, a brown sweater and olive-green trousers, the blond defendant fiddled with a bracelet, speaking very quietly as he pleaded not guilty to raping four women. He later removed his sweater and sat in a plain, white T-shirt.