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

Prince Frederik of Luxembourg, who died at 22, spoke about the rare genetic disorder he navigated in a video released by The PolG Foundation he founded.

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.