Prince Mangosuthu Buthelezi has announced that King Goodwill Zwelithini has died in hospital on Friday morning.
The King had been in hospital for weeks for what was initially reported to be a problem with his blood glucose levels.
The royal house said his health took a turn for the worst and he passed away in the early hours of Friday morning.
“It is with the utmost grief that I inform the nation of the passing of His Majesty King Goodwill Zwelithini,” he said in a short statement.
“On behalf of the royal family, we thank the nation for your continued prayers and support in this most difficult time,” the statement read.
He was 72 years old.
King Zwelithini became king on the death of his father, King Cyprian Bhekuzulu kaSolomon, in 1968, at only age 20.
But – he was not crowned until 1971 – because he had to go into hiding outside the kingdom following a plot to have him killed.