Princess Martha, 48, posted a picture of a smiling Ari Behn and an emotional tribute on her Instagram account: "Dear Ari, We were supposed to be together at Christmas and celebrating. We had all been looking forward to it."
"And we are so infinitely sad and sorry for the loss of just you, because you were the girls' warm, funny, wise and good dad that they so dearly miss.
"We miss the funny comments, your fine viewpoints, the poetic tone, the overflowing compliments, the great love you had for them.... You are and will continue to be deeply missed, Ari." It got 67, 615 likes.
One follower wrote: "I met Ari Ben in Gardermoen airport... I thought he was a very polite and good person... I wish all the love for your daughters, that all the love you left in them flourish in their hearts. Now they have an angel who will take care of your precious daughters."
"You... write fine about their father. You are you, he was himself and everyone else is us who thinks so much about everything. Keep trusting yourself," read another remark.
The former Norwegian royal Ari Behn battled alcoholism and "devouring anxiety".
In 2017, he accused actor Kevin Spacey of groping him under a table. Ari Behn, 47, and Martha divorced in 2017.
( With inputs from IANS )