The duchess, 62, and Ms. Barankitse, 60, have become so close that they refer to each other as “my sister.”

On March 26 and 27, they will meet in Luxembourg when the duchess sponsors a two-day international conference on the fight against rape — as a weapon of war and a byproduct of mass migration and political instability. The duchess organized the conference with Dr. Denis Mukwege, the Congolese gynecologist who specializes in the treatment of women raped in war and conflict, and who, with Nadia Murad, won the Nobel Peace Prize in 2018.

The conference, “Stand Speak Rise Up!” will hear testimony from some of the 40 rape survivors coming from war-ravaged countries, including Syria, the Democratic Republic of Congo, Kosovo and Rwanda. The survivors will join leading crusaders for change, including Ms. Murad and Dr. Mukwege; Céline Bardet, a founder of We Are Not Weapons of War, an NGO that provides support for victims of rapes in conflict; and Muhammad Yunus, the Nobel Peace Prize winner for 2006.

“I admit this is not at all a usual cause for the wife of a royal,” the duchess said in an interview from Luxembourg. “But I have made it my responsibility to take on the causes no one wants to talk about. The survivors had no platform from which to speak. We are giving them a voice.”

In an interview from Kigali in Rwanda, Ms. Barankitse agreed. “The survivors of rape will stand before these great personalities, before the world, and be recognized,” she said, speaking in French. “It can help give them back their dignity.”