Saudi King Salman has appointed Interior Minister Mohammed bin Nayef as his new heir and made his son, Defence Minister Mohammed bin Salman, second-in-line to succeed in a dramatic reshuffle in the world’s top oil exporter. By making Mohammed bin Nayef, 55, crown prince, and Mohammed bin Salman, who is thought to be in his early 30s, deputy crown prince, the Saudi monarch has set the kingdom’s succession in stone for decades and strengthened his branch of the dynasty.