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

The young prince, who is the son of Prince Robert of Luxembourg and Princess Julie of Nassau, was diagnosed with POLG mitochondrial disease at 14. The life expectancy of someone with the genetic disease is short, and the disorder currently has no cure.

“Frederik fought his disease valiantly until the very end,” his father shared in his statement. “His indomitable lust for life propelled him through the hardest of physical and mental challenges.”

According to the POLG Foundation, which Frederik founded, the disease “robs the body’s cells of energy, in turn causing progressive multiple organ dysfunction and failure.”

“One might compare it to having a faulty battery that never fully recharges, is in a constant state of depletion and eventually loses power,” Robert added.

Robert detailed his son’s goodbyes to family members, saying that he found “the strength and the courage to say goodbye” on Feb. 28, which is also Rare Disease Day.

“Even in his last moments, his humor, and his boundless compassion, compelled him to leave us with one last laugh, to cheer us all up,” Robert said.

“Frederik’s last question to me, prior to his other remarks was: ‘Papa, are you proud of me?’” Robert said of the heartbreaking moment.

“He had barely been able to speak for several days, so the clarity of these words was as surprising as the weight of the moment was profound,” the royal explained.

“The answer was very easy, and he had heard it oh so many times … but at this time, he needed reassurance that he had contributed all that he possibly could in his short and beautiful existence and that he could now finally move on.”

His family shared that Frederik died in Paris, also known as “the City of Lights.”

“One light was extinguished, but so many remain,” his father wrote.

Frederik is survived by his parents as well as his two siblings: his brother, Alexander, and his sister, Charlotte.