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 of Luxembourg, the youngest son of Prince Robert of Luxembourg and Princess Julie of Nassau, has died after a lifelong battle with a rare genetic disorder known as POLG mitochondrial disease.

Prince Frederik, 22, was a founder and the creative director of a foundation that raised awareness of POLG disorder.