London (CNN) Fashion designer Khalid Al Qasimi, the 39-year-old son of the ruler of Sharjah in the United Arab Emirates (UAE), has died in circumstances described by UK authorities as unexplained.

The Emirate of Sharjah announced the death in a statement Tuesday after London's Metropolitan Police were called to a residence in the upmarket Knightsbridge area shortly after 10.30 a.m. local time (5.30 a.m ET) the day before.

"A man in his late 30s was found deceased inside the property," the police said in a statement, adding that the "death is currently being treated as unexplained." A post-mortem examination carried out Tuesday failed to identify the cause of death, it added. British media said the body was that of Qasimi.

Funeral prayers were held for Sheikh Khalid bin Sultan Al Qasimi on Wednesday as the emirate announced three days of mourning, with flags flying at half staff.

His father, Sheikh Sultan bin Muhammad Al Qasimi, posted images and a video of the prayers on Instagram Wednesday.