Marius Borg Høiby was arrested on Sunday evening and is accused of assault, threats with a knife and violation of a restraining order, police said in a statement.
Norwegian media quoted police as saying the offences took place over the weekend.
On Monday, the Oslo district court granted their request to keep him in detention for up to four weeks on the grounds of a risk of reoffending.
Defence lawyer Petar Sekulic told The Associated Press the arrest followed an alleged "incident" involving another person on Sunday.
He declined to give details, but said Høiby contests his detention and his legal team was considering an appeal as soon as he and the other person can provide statements to police.
With his trial opening on Tuesday, police won't be able to hear those statements any sooner than this weekend, when the proceedings take a scheduled break, Sekulic said.
On Tuesday, Høiby faces an indictment including 38 counts at the Oslo court.
They include rape, abuse in a close relationship against one former partner, acts of violence against another and transporting 3.5kg of marijuana. Other charges include making death threats and traffic violations.
Høiby has been under scrutiny since he was repeatedly arrested in 2024 on various allegations of wrongdoing. He was indicted in August, but had been free pending trial until Sunday.
Høiby is the son of Crown Princess Mette-Marit from a previous relationship and stepson of the heir to the throne, Crown Prince Haakon. He has no royal title or official duties.
The indictment centres on four alleged rapes between 2018 and November 2024; alleged violence and threats against a former partner between the summer of 2022 and the fall of 2023; and two alleged acts of violence against a subsequent partner, along with violations of a restraining order.
Høiby's defence team has said that he "denies all charges of sexual abuse, as well as the majority of the charges regarding violence".
Haakon said last week that he and Mette-Marit don't plan to attend court and the royal house doesn't intend to comment during the proceedings, which are scheduled to last until March 19.
He emphasised that Høiby isn't part of the royal house and that, as a citizen of Norway, he has the same responsibilities and rights as all others. He said that he's confident that all concerned will make the trial as orderly, proper and fair as possible.
While the royals are generally popular in Norway, the Høiby case has cast a shadow on their image. And the trial is opening just as his mother faces renewed scrutiny over her contacts with Jeffrey Epstein.
Friday's release of the latest batch of documents from the Epstein files shone an unflattering spotlight on Mette-Marit. They contained several hundred mentions of the crown princess, who already said in 2019 that she regretted having had contact with Epstein, Norwegian media reported.
The newly released documents, which include email exchanges with Epstein, showed that Mette-Marit borrowed a property of Epstein's in Palm Beach, Florida, for several days in early 2013, and the royal house confirmed that she did so through a mutual friend, broadcaster NRK reported.
In a statement emailed by the royal house, Mette-Marit said that she "must take responsibility for not having investigated Epstein's background more thoroughly, and for not realizing sooner what kind of person he was."
"I deeply regret this, and it is a responsibility I must bear. I showed poor judgment and regret having had any contact with Epstein at all," she said.
"It is simply embarrassing."
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