A former wife of Saudi Arabia's billionaire king has appealed to Barack Obama for help freeing the four adult daughters she says have been held in a Saudi royal palace against their will for over a decade.Alanoud AlFayez, 57, made her public plea to the president on Thursday, just a day before he's scheduled to visit King Abdullah for just the second time.'Mr Obama should take this opportunity to address these grave violations committed against my daughters,' said AlFayez. AlFayez, 57, a Jordanian national who has lived in London since her divorce from the Saudi monarch in 2003,said her children needed to be "saved".