The son of the Ruler of Sharjah has died, the emirate's Ruler's Court announced on Tuesday.
Sheikh Khalid bin Sultan Al Qasimi died on Monday in London, said Sharjah Media Office. He was 39.
The Ministry of Presidential Affairs said President Sheikh Khalifa ordered three days of national official mourning, beginning when the body is repatriated, with flags to be flown at half mast.
The Ruler's Court of Sharjah said funeral prayers would be held at 9am on Wednesday at King Faisal Mosque in the emirate.
The court offered its condolences to Sheikh Dr Sultan bin Muhammad Al Qasimi, Ruler of Sharjah, and Al Qasimi family.
Sheikh Khalid was the chairman of Sharjah Urban Planning Council. He also led work on Sharjah Architecture Triennial, an exhibition and series of events held every three years.
Sheikh Khalid was the creative director and co-owner of a British fashion label, Qasimi, whose debut collection premiered in 2008.
He moved to the UK aged 9 and studied at Tonbridge School in Kent. He went on to study French and Spanish at University College London and earned a degree in architectural studies at the Association School of Architecture, according to the Qasimi company website.
Sheikh Mohammed bin Rashid, Vice President and Ruler of Dubai, offered his support to the Ruler of Sharjah on Tuesday.
"I present my sincere condolences to my brother Sheikh Sultan bin Mohammed Al Qasimi on the death of his son Sheikh Khalid bin Sultan," said Sheikh Mohammed on Twitter.
"I also send my sincere condolonces to the sons and daughters of Sharjah and the UAE. I ask God to give my brother Sheikh Sultan patience during this difficult time.
"We saw in you affection and compassion for everyone from this country, and we felt your big heart. I pray to God that he may give you strength during this time."
Sheikh Mohamed bin Zayed, Crown Prince of Abu Dhabi and Deputy Supreme Commander of the Armed Forces, also offered his condolences to Sheikh Dr Sultan.
“We received the news of the death of our son, Sheikh Khalid bin Sultan Al Qasimi, may God rest his soul, with great sadness and sorrow,” he said in a tweet.
“We extend to our dear brother Sheikh Sultan bin Muhammad Al Qasimi and Al Qasimi family our sincere condolences.”
Tributes and messages of condolences flooded in on social media from across the country with many praying that God rest his soul and offering their sympathies to Sheikh Dr Sultan.
Users tweeted pictures of the father and son together, as well as photos of Sheikh Khalid with his brother, Sheikh Mohammed bin Sultan, who died 20 years ago.
Patrick Moody, the British ambassador to the UAE, tweeted his "deepest condolences" to Sheikh Dr Sultan and his family.
Sheikh Dr Sultan shared the announcement of his youngest son's death on Instagram, posting the statement from the Ruler's Court with a black and white photo of Sheikh Khalid.
"Sheikh Khalid bin Sultan bin Muhammad Al Qasimi is in the care of God," the post read.