Adam Shand Kydd, the late Princess Diana's stepbrother, was found dead inside his rented apartment in Phnom Penh, Cambodia, a report said in Bangkok on Wednesday.
Cambodian police found the 50-year-old Kydd's body on Monday and suspect drug overdose as the cause of death, it said.
Earlier, British embassy officials told the Cambodian police that Kydd had royal connections.
Princess Diana's mother left Earl Spencer and married Peter Shand Kydd in 1969. Earl Spencer won custody of Diana and her siblings.