Answer
Muhammad bin Nayef was the Crown Prince of Saudi Arabia from 2015 to 2017. He was appointed by his half-brother, King Salman, after the death of the previous Crown Prince, Nayef bin Abdulaziz. Muhammad bin Nayef was a close ally of Salman and was seen as a likely successor to the throne. However, he was removed from the position of Crown Prince in 2017 and replaced by Muhammad bin Salman.