Saudi Arabian crown prince Nayef Bin Abd Al-Aziz, designated heir to King Abdullah Bin Abd Al-Aziz, died Saturday in Geneva, where he was receiving medical treatment. Nayef, 78, headed the country’s ministry of interior and was deputy premier in the royal cabinet. He was named crown prince last year.

President Barack Obama expressed “great regret” at the death of the crown prince, and praised his “leadership [under which] the United States and Saudi Arabia developed a strong and effective partnership in the fight against terrorism.” Vice President Joe Biden said that he was “saddened” by the news, and had “looked forward to welcoming [Nayef] to the United States.”