The young prince struggled with the incurable disease since he was 14. The royal family of Luxembourg is currently in mourning, as Prince Frederik of Luxembourg—the youngest son of Prince Robert of Luxembourg and Princess Julie of Nassau—has died at 22 from complications of a rare genetic disorder called POLG mitochondrial disease.

P rince Frederik of Luxembourg, the youngest son of Prince Robert of Luxembourg and Princess Julie of Nassau, died in Paris at age 22 on March 1—a day after Rare Disease Day—of a rare genetic disease known as POLG.

Prince Frederik, the son of Europe's Prince Robert of Luxembourg, has died from a rare genetic disease, his family announced.