Author and the King of Norway's former son-in-law, Ari Behn, passed away aged 47, according to his spokesman.
Behn took his own life, his spokesman told Norway's NTB agency.
The writer - also Princess Martha Louise’s former husband - had accused Hollywood actor Kevin Spacey in December 2017 of groping him after a Nobel Peace Prize concert. Spacey did not respond to the allegation, which was one of many at the time.
Coincidentally, he is the third Kevin Spacey accuser to die since allegations of sexual harassment surfaced against the actor.
The Norwegian royal family said in a statement that he had been "an important part of our family for many years and we carry warm and good memories of him with us."
"We are grateful that we got to know him," King Harald and Queen Sonja added. "We grieve that our grandchildren have now lost their beloved father."