His father announced the news on the POLG foundation website

The cousin of Henri, Duke of Luxembourg, who shocked the world with his abdication last year, revealed his son died on March 1, following a long battle with rare genetic condition, POLG Mitochondrial disease.

He announced the news in a lengthy, heartfelt message posted to the POLG foundation, a website founded by his son, and dedicated to finding effective treatments and a cure for POLG mitochondrial disorders.

POLG disease is a rare genetic disorder that robs the body’s cells of energy, in turn causing progressive multiple organ dysfunction and failure.

Progression of the condition can cause multiple organs to fail, such as the brain and liver, as well as the intestines, muscles, and swallowing functions to falter.

Prince Frederik, who lived in Switzerland, was born with the disease, though official diagnosis occurred much later at age 14.

In a statement written by Prince Robert, 69, and his wife, Princess Julie of Nassau, 64, they revealed their son's heartbreaking last moments, which included a final goodbye to his parents and two siblings, Princess Charlotte of Nassau, 29 and Prince Alexandre of Nassau, 27.

It read: "It is with a very heavy heart that my wife and I would like to inform you of the passing of our son, The POLG Foundation Founder and Creative Director, Frederik."

He revealed that his son had said his final goodbyes on 'Rare Disease Day' which takes place the last Friday in February.

He continued: "Last Friday, February 28th, on “Rare Disease Day”, our beloved son called us in to his room to speak to him for one last time.

"Frederik found the strength and the courage to say goodbye to each of us in turn – his brother, Alexander, his sister, Charlotte, me, his three cousins, Charly, Louis, and Donall, his brother-in-law, Mansour, and finally, his Aunt Charlotte and Uncle Mark. 

"He had already spoken all that was in his heart to his extraordinary mother, who had not left his side in 15 years. After gifting each of us with our farewells – some kind, some wise, some instructive – in true Frederik fashion, he left us collectively with a final long-standing family joke. 

"Even in his last moments, his humour, and his boundless compassion, compelled him to leave us with one last laugh….to cheer us all up."

He shared that his son fought valiantly with the condition until the end, adding that he did so 'with grace and with humour'.

Prince Frederick of Nassau was born in Aix-en-Provence, France, and enjoyed a stint in London, England, before moving to Switzerland in 2004. 

The former student attended the International School in Geneva, Ecole Eden primary school and St George’s School in Clarens.

His father, Prince Robert of Luxembourg, is the first cousin of Grand Duke Henri of Luxembourg, 69, who in December announced his shock abdication from the throne in favour of his son Guillaume.

Guillaume will formally take up his new title on October 3, 2025.