27-year-old Marius Borg Høiby was arrested late on Friday in a cabin north of Lillehammer. The police say that he has violated a restraining order and that there is a "risk of repetition".
On Saturday afternoon, he was released, according to the police without being questioned.
We made it clear to him that new violations of the restraining order will have consequences, says Andreas Kruszewski, prosecutor at the police.
According to him, it may involve detention or electronic surveillance.
According to Borg Høiby's lawyer Øyvind Bratlien, he is accused of having contacted his former girlfriend from a hidden phone number.
He should never have been arrested, says Bratlien.
"He denies this and does not admit guilt. During my 17 years as a defense attorney, I have not experienced or heard of an arrest on such a thin factual and legal basis", the lawyer wrote in a text message to the news agency NTB before the release.
High priority
The police write in a statement that the investigation against Borg Høiby is growing and that he is now, in addition to violating the restraining order, suspected of committing a crime against another person. It is alleged to be unlawful threats.
"Currently, there are four victims in the case. The Oslo police are investigating the case with high priority", according to the police.
Violence in close relationships always has high priority, says Andreas Kruszewski.
Lawyer Petter Grødem, who represents one of the former girlfriends, says that his client is disappointed that Borg Høiby has not commented on the allegations.
We think it's high time now, he says to NRK.
For my client, it's not so important what he's accused of, it hasn't been her point. What's important for her is that the truth comes out so that others don't experience the same thing.
Drug problems
Borg Høiby was initially arrested on August 4 after an incident in an apartment in Oslo. He is accused of, and has admitted to, assaulting his girlfriend and is subject to a restraining order.
He is also being investigated for a number of other crimes, including threats, vandalism, theft of an electric scooter, and assault of two former girlfriends.
The 27-year-old, who is the son of Mette-Marit from a previous relationship, has stated in a written statement that he has problems with alcohol and drugs.
The Norwegian royal couple has so far refused to comment on the allegations.