Marius Borg Høiby, the eldest son of Norwegian Crown Princess Mette-Marit, must remain in pre-trial detention for a further four weeks, an Oslo court ruled on Monday.
The 29-year-old will continue to serve the detention under house arrest with an ankle tag, the news agency NTB reported.
Høiby was sentenced to four years in prison in June, though the verdict has not yet become final.
He was found guilty of two counts of rape and violence against a former girlfriend.
A restraining order is in place to protect her, which Høiby has already violated on several occasions.
Police argued there was a risk of Høiby committing further offences and requested an extension of the house arrest. The court agreed.
Høiby sought release on condition that he stay away from certain areas, but the court rejected his application.
NTB cited Høiby’s defence lawyer, Petar Sekulic, as saying that he would now review the court’s decision together with Høiby and consider a possible appeal.
The extended pre-trial detention runs until September 7. Høiby is permitted to leave his residence for purposes such as medical appointments or visiting sick family members. He must also submit to regular drug tests.