He recounts his grief at the death of his younger brother Alfonso when the two were "playing" with a pistol as teenagers at their family's home in Portugal in 1956, a case that has never been fully investigated.
More than 65,000 people have fled El-Fasher since its fall, including more than 5,000 who are now sheltering in Tawila, which was already hosting more than 650,000 displaced people, according to the UN.
In a personal piece released by his US office, the prince said he had witnessed "courage and compassion in the harshest conditions imaginable" during his time in the armed forces.