Sunnis in the Arab world reserve the term sharif/sherif or shareef for descendants of Hasan ibn Ali, while sayyid is used for descendants of Husayn ibn Ali, Hasan's younger brother. Both Hasan and Husayn are grandchildren of the Islamic Prophet Muhammad, through the marriage of his cousin Ali and his daughter Fatima. However, since the post-Hashemite era began in 1925 after the fall of the Sharif of Mecca, the term sayyid has been used to denote descendants from both Hasan and Husayn.