Crown Prince Sultan Bin Abdulaziz, the heir to the Saudi throne, died in the U.S. on Sunday.
According to a leaked U.S. diplomatic cable, Abdulaziz was being treated for colon cancer. His body is expected to be returned to Saudi Arabia late Monday, the Arabic daily Asharq Alawsat reported.
President Barack Obama joined other world leaders in extending condolences "on behalf of the American people."
He called Abdulaziz a "valued friend" who helped strengthen ties between the U.S. and Saudi Arabia.
"He was a strong supporter of the deep and enduring partnership between our two countries, forged almost seven decades ago," Obama said.
"As minister of defense and aviation for almost 50 years, Crown Prince Sultan dedicated himself to the welfare and security of his people and country and was a valued friend of the United States," the president said.
The most likely person to take his place in line for the Saudi throne is Prince Nayef, King Abdullah's half brother and current interior minister.
The Saudi alliance with the U.S. is expected to remain intact no matter who succeeds Abdullah. Saudi Arabia is seen as a key U.S. ally in the Middle East.