Saudi Arabia's Crown Prince Sultan bin Abdul-Aziz has died of an undisclosed illness. He was in his eighties.

His death was announced by the Saudi media, which said he died Saturday “outside of the kingdom following an illness.”

Western news reports say he died while undergoing medial treatment in the United States.

Crown Prince Sultan was one of the kingdom's most powerful figures and was believed to be first in line to the throne. He was the half brother of King Abdullah.

In late 2010, he governed the kingdom while King Abdullah underwent surgery in New York.

Both the monarch and the crown prince have suffered health problems in recent years.

In 2009, Prince Sultan received treatment in the U.S. for an undisclosed illness. Prior to the visit, he had been diagnosed with cancer.

The crown prince had served as Minister of Defense and Aviation since 1963. According to the Saudi embassy to the U.S., he was instrumental in establishing the kingdom's modern armed forces.

He had previously served as Minister of Transportation and governor of Riyadh.

Saudi news reports say Prince Sultan's funeral will take place on Tuesday.