Mohammed Bin Nayef, who once headed the country's security apparatus, was reportedly told that an alleged "addiction to painkillers" made him unsuitable for office.According to palace sources cited by Reuters, King Salman himself delivered the unexpected blow to Bin Nayef at the palace."The king came to meet MBN [Mohammed bin Nayef] and they were alone in the room. He told him: 'I want you to step down, you didn't listen to the advice to get treatment for your addiction which dangerously affects your decisions'," Reuters quoted a source close to the former crown prince as saying."It was a big shock to MbN," the source added. "It was a coup. He wasn't prepared."The drug addiction mentioned by the king is thought to refer to Bin Nayef's reported reliance on medication since an assasination attempt in 2009 by a suicide bomber. The attack left the prince, who also suffers from diabetes, injured and scarred.Having sprung the coup on the prince so close to the Eid feast, the plotters reportedly played on his physical and mental weakness to wear him down into the early hours of the morning. Bin Nayef, a New York Times source says, conceded to their demands in the morning, when it was finally announced that his 31-year-old cousin, Mohammed Bin Salman, would be the new heir.At the time, the move was presented publicly as a smooth transition, with the younger prince shown kissing the hands and feet of his elder cousin."Good luck, God willing," Bin Nayef was recorded as saying to his Bin Salman.Despite the Saudi court's best efforts to paint the handover as a smooth transition, speculation was rife at the time about a palace coup The new accounts given by US intelligence staff and individuals close to the Saudi court have confirmed this widely held suspicion.This was especially so given that Bin Nayef - an experienced politician who had overseen the crushing of al-Qaeda in Saudi Arabia - was now replaced by his younger, inexperienced cousin who had built up a reputation for brashness and lack of political acumen.Bin Nayef himself had reservations about Bin Salman's capabilities, particularly over his reckless and costly war in Yemen and cutting of public sector benefits.It is also thought that Bin Nayef was opposed to the isolation of Saudi Arabia's neighbouring Qatar - a stance which perhaps hastened his fall.