Saudi Arabia's King Abdullah has appointed the kingdom's powerful Interior Minister and his half-brother as the nation's second Deputy Prime Minister, according to an announcement late Friday. The appointment indicates a succession order in the royal family, after four years of speculation over who will be the next-in-line once current heir, Prince Sultan, becomes king. A royal statement carried by the official SPA news agency says Prince Nayef will take over the post, which is seen as a crown-prince-in-waiting. The Saudi Constitution does not require the king to appoint a second Deputy Prime Minister but Friday's move is also important because it will allow the king to travel abroad. With Prince Sultan away in the United States on medical treatment, Prince Nayef's appointment will ensure that when the king goes to the Arab Summit in Qatar next week and later to the G-20 meetings, somebody will be in charge at home. However, Prince Nayef's appointment as second to the throne will still have to go through the Allegiance Association, set up by the king in 2006 and composed of his brothers and some of his nephews who all vote by a secret ballot to choose future kings and crown princes. The Allegiance is expected to have the final say on who becomes crown prince after Sultan, who is in his 80s.