Mohammad Reza was born along with his twin sister, Ashraf. However, Shams, Mohammad Reza, Ashraf, Ali Reza, and their older half-sister, Fatimeh, were not royalty by birth, as their father did not become Shah until 1925. Nevertheless, Reza Khan was always convinced that his sudden quirk of good fortune had commenced in 1919 with the birth of his son who was dubbed "khoshghadam" (bird of good omen). Like most Iranians at the time, Reza Khan did not have a surname and after the 1921 Persian coup d'état which deposed Ahmad Shah Qajar, he was informed that he would need a name for his house. This led Reza Khan to pass a law ordering all Iranians to take a surname; he chose for himself the surname Pahlavi, which is the name for the Middle Persian language, itself derived from Old Persian. At his father's coronation on 24 April 1926, Mohammad Reza was proclaimed Crown Prince.