(CNN) -- Saudi Crown Prince Nayef bin Abdulaziz has died, Saudi state TV said on Saturday.
Nayef, who had been named crown prince in October by his brother the king, was heir to the Saudi throne.
State TV is broadcasting Quran readings as an expression of mourning for the prince, who died in Geneva, Switzerland.
"The news of Prince Nayef bin Abdulaziz death was shocking to everyone in the Kingdom and to the royal family," Saudi Foreign Ministry spokesman Osama Nogali told CNN. "We still don't know the reason behind his death."
Nayef's body will arrive in Jeddah, Saudi Arabia Sunday and will be buried after afternoon prayer, Nogali said.
The crown prince served as Saudi interior minister since 1975, having overseen the kingdom's counterterrorism efforts.
He also served as deputy premier.
A classified U.S. Embassy cable leaked by the website WikiLeaks described Nayef as a hard-line conservative who was lukewarm to King Abdullah's reform initiatives.