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.

The son of Prince Robert of Luxembourg and Princess Julie of Nassau, Prince Frederik, has died in Paris the age of 22 due to a rare genetic disorder – POLG Mitochondrial disease. At such a critical moment in US history, we need reporters on the ground. Your donation allows us to keep sending journalists to speak to both sides of the story.