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.

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.

The prince had PolG disease, a genetic mitochondrial disorder that prevents the body's cells from producing adequate energy.