Prince Sisowath Thomico, a royal family member who also was Norodom Sihanouk's assistant, said his death was "a great loss to Cambodia," adding that he had dedicated his life "for the sake of his entire nation, country and for the Cambodian people."
Sihanouk's successor, Norodom Sihamoni, is expected to fly to Beijing on Monday to retrieve his father's body, Thomico said.
Cambodian government spokesman Khieu Kanharith said an official funeral will be held once the former King's body is repatriated.
Norodom Sihanouk, the former Cambodian king who remained an influential figure in his country's politics through a half-century of war, genocide and upheaval, has died aged 89.
Cambodian government spokesman Khieu Kanharith said Sihanouk died of natural causes in Beijing, where he had travelled to for medical treatment earlier this year.
Prince Sisowath Thomico, a royal family member who was also Sihanouk's assistant, said the former King suffered a heart attack at a Beijing hospital.
Cambodia's former King Norodom Sihanouk has died in Beijing, according to Reuters.