On April 5, Nina Lagergren passed away at the age of 98.Nina was Raoul Wallenberg’s younger half-sister, born nine years after him.Their mother, Maria “Maj” Sofia Wising married Fredric von Dardel six years after the death of Raoul’s biological father.The new couple had two children, Guy von Dardel, born in 1919, and Nina.I had the rare privilege to know both of them. They were different in nature but shared a deep love for their elder brother, who in 1945 became a tragic hero.In fact, by the young age of 32, Raoul Wallenberg had managed to save scores of Hungarian Jews during WWII, in a daring mission that lasted eight months. When the war was approaching its end, Raoul decided to hold a meeting with the Soviet military in order to coordinate relief efforts for the Jewish survivors in the aftermath of the Holocaust. Instead, he was abducted, transferred to Moscow, and ever since his fate has been shrouded in mystery.Guy von Dardel grew up to become a renowned physicist. Alongside his brilliant career he dedicated a great part of his adult life to rescue his brother, leaving no stone unturned.In the latter part of his life I accompanied him in his efforts, and saw first-hand his anguish mixed with hope. Alas, he passed away in 2009, heartbroken, for he was not able to retrieve his brother back home. After his death, I and the International Raoul Wallenberg Foundation, which I had the privilege to found decades earlier, continued to collaborate with Guy’s widow, Matti, and their daughters Marie Dupuy and Louise de Dardel.Nina had a different nature. She was a soft-spoken woman, more prone to believe in quiet diplomacy, who dedicated most of her energies to keep alive the wonderful legacy of her half-brother through educational activities and the help of her grandchildren.Few know, perhaps, that Nina was the mother-in-law of the late UN secretary-general Kofi Annan, who was married to Nina’s daughter, Nane Annan.The last time I saw Nina was on July 9, 2014. I vividly remember that day. Many months earlier, the Wallenberg Foundation had started mustering bipartisan support for the idea of posthumously bestowing the Congressional Gold Medal to Raoul Wallenberg. This effort came to fruition, and on that day at the US Capitol Rotunda we were moved to tears when Nina Lagergren received the medal on behalf of Raoul from the hands of the 53rd speaker of the House of Representatives, John Boehner.She then gave a brief speech, which reverberates even today in my mind. Her most powerful message was: “We honor him for what he did, but we must honor him for what we can do for him. There must be a way for us to come together. Everyone can do something, and we are all so important in this world”.Regrettably, Nina Lagergren could not achieve her dream. She was an intelligent, humble and lovable human being with an inner strength rarely seen.She left a powerful message of love and understanding, and I see myself obliged to continue her struggle to bring Raoul back home and to keep alive his remarkable legacy.The writer is founder of the International Raoul Wallenberg Foundation.