to succeed his great grandmother Queen Elizabeth II, the head of state of the United Kingdom and 15 other Commonwealth realms, including Australia and Canada.
The baby will follow its grandfather Prince Charles, the heir to the throne, and its father Prince William, the eldest child of Charles and the late Diana, princess of Wales.
Royal family: House of Windsor.
Prince William and Kate with their newborn son Prince George Alexander Louis. (AP Photo)
Princess Elisabeth, aged 11, is the heir to the throne. Her father King Philippe -- who is married to Princess Mathilde d'Udekem d'Acoz -- became king on Sunday after his father Albert II abdicated.
After Philippe's eldest daughter, who could become the first queen of the Belgians, their three other children follow -- Gabriel, nine, seven-year-old Emmanuel, and Eleonore, five. The law excluding women from becoming the monarch was repealed in 1991.
Royal family: House of Belgium.
King Philippe of Belgium, his wife Queen Mathilde and children (from L) Princess Eleonore, Prince Gabriel, Princess Elisabeth and Prince Emmanuel at the Royal Palace in Brussels.(AFP Photo)
Crown Prince Frederik of Denmark with Prince Vincent, crown Princess Mary, Princess Josefina, and Prince Christian and Princess Isabella, in Copenhagen. (AP Photo)
Prince Christian, seven, is second in line to the throne after his father, Crown Prince Frederik, the eldest son of Queen Margrethe II and Prince Consort Henrik.
He comes before his sister Isabella, six, third in line to the throne. The law which excluded women from the succession was repealed in 1953.
Royal family: House of Oldenburg.
Prince Hisahito, six, the only son of Prince Akishino (the younger brother of Crown Prince Naruhito), is third in line to the throne after his uncle and father, the children of Emperor Akihito.
Princess Aiko, the 11-year-old only child of Naruhito and his wife Masako, is not in line to inherit the throne as females were excluded in 1889.
Royal family: Yamato Dynasty
Prince Hisahito (C), holding a certificate of graduation and accompannied by his father Prince Akishino (L) and mother Princess Kiko, poses for photos in Tokyo. (AFP Photo)
Prince Moulay Hassan, 10, the son of King Mohammed VI and Princess Lalla Salma, is the kingdom's crown prince. He has a sister, six-year-old Lalla Khadija, who is ruled out of the succession as a girl.
Royal family: Alawi Dynasty
Morocco's King Mohammed VI (R) sits beside his son Crown Prince Moulay Hassan III (C) and his brother Moulay Rachid (L)in Rabat. (AFP Photo)
Princess Catharina-Amalia, nine, the oldest child of King Willem-Alexander and Queen Maxima, is first in line to the throne. She is followed by her sisters Alexia, eight, and Ariane, six. Under a 1983 law the eldest son or daughter becomes heir.
Royal family: House of Orange-Nassau.
Dutch Princesses Alexia and Ariane and Princess of Orange Catharina-Amalia pose at the Royal Palace in Amsterdam. (AFP Photo)
Crown princess Mette-Marit with Princess Ingrid Alexandra, crown princess Mette-Marit's son Marius Borg Hoiby, and Queen Sonja with Prince Sverre Magnus on her lap. King Harald and crown prince Haakon (background). (AFP Photo)
Princess Ingrid Alexandra, nine, the first daughter of Crown Prince Haakon and Crown Princess Mette-Marit, is second in line to the throne.
She is followed by her seven-year-old brother Sverre Magnus. Since 1990, the eldest child assumes succession, whether a boy or a girl.
Royal family: House of Oldenburg.
Seven-year-old Leonor de Borbon, is second in line to succeed King Juan Carlos of Spain, after her father, Crown Prince Felipe.
The Spanish constitution currently allows a female heir to the throne only if she has no brothers.
If she does not have a brother, Leonor could become the first female Spanish head of state since Isabelle II (1833-1868). Her six-year-old sister Sofia is third in line to the throne.
Royal family: House of Bourbon.
Princess Letizia, her daughter Sofia, Prince Felipe, Leonor and Queen Sofia pose before the baptism ceremony of Sofia de Borbon at Zarzuela Palace in Madrid in 2007. (AFP Photo)
Princess Estelle, the daughter of Sweden's Crown Princess Victoria and Prince Daniel, who is 17-month-old, is second in line to the throne, after her mother, the daughter of King Carl XVI Gustaf. In Sweden, male primacy was abolished in 1980.
Royal family: House of Bernadotte.
Sweden's crown princess Victoria and Prince Daniel with Princess Estelle to the Royal church in Stockholm. (AFP Photo)