He was also the ruler of Abu Dhabi emirate.
“The Ministry of Presidential Affairs condoles the people of the UAE, the Arab and Islamic nation and the world over the demise of His Highness Sheikh Khalifa bin Zayed Al Nahyan, the president of the UAE,” read a statement by state news agency WAM in Twitter.
According to the statement, the country will “observe a forty-day state mourning with the flag flown at half-mast starting today” while also announcing three days of nationwide holidays as all ministries, departments, and federal, local and private entities will suspend work.
It was several years that Sheikh Khalifa was suffering illness which had long prevented him from appearing before the public and involving in day-to-day affairs.
According to the UAE constitution, Vice-President and Prime Minister Sheikh Mohammed bin Rashid Al Maktoum, the ruler of Dubai, will act as president until the federal council, consisting of the rulers of the seven emirates, meets within 30 days to elect a new president.
Born in 1948, Sheikh Khalifa became the second president of the UAE in November 2004 succeeding his father as the 16th ruler of Abu Dhabi.
He is expected to be succeeded as the ruler of Abu Dhabi by his half-brother Crown Prince Sheikh Mohammed bin Zayed Al Nahyan, who suffered a stroke in 2014, following which he has rarely been seen in public, although he has continued to issue rulings.