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 of Luxembourg died at the age of 22 due to a rare mitochondrial condition called POLG disease— Newsweek has rounded up what you need to know about the illness. The European royal died in Paris on March 1, one day after "rare disease day," according to his father Prince Robert of Luxembourg's public announcement.

Prince Frederik of Luxembourg died on March 1, his family wrote in an emotional statement last week. He was 22.