Some had hoped that Willam and Kate's child would be a little girl as it would be the first time an heir's eldest child would inherit the throne regardless of its gender. Given that there are already five young female heirs to thrones across Europe, however, Prince George is actually in the minority as a boy.
Denmark, Japan and Morocco are the other three countries with male heirs. In Denmark, Prince Christian, seven, stands second in line to the throne after his father, Prince Frederik.
Christian, who's grandmother is the current sovereign, Queen Margrethe, is the eldest of Frederick and Princess Mary's four children.
From left to right: Prince Christian of Denmark, Prince Moulay Hassan of Morocco and Prince Hisahito of Japan
Similar to the reaction caused by Kate's pregnancy, the possibility that Princess Mary could have a female child motivated the Danish government to change the constitution permitting Mary and Frederick's first-born to inherit the throne irrespective of its sex.
In Japan, Prince Hisahito of Akishino is heir to the Chrysanthemum throne. The Prince, six, graduated from kindergarten in March and now attends Ochanomizu University Elementary School, which is located in Tokyo's educational Bunkyo district.
Given that the country's constituton dictates that only males can accede the Japanese throne, Prince Hisahito is not the direct heir of Emperor Akihito. Princess Aiko, who is Akihito's granddaughter, is not included in the Japanese line of sucession after her father, Prince Naruhito.
From left to right: Princess Leonor of Spain, Prince Cathatina-Amalia of the Netherlands, Princess Estelle of Sweden and Princess Ingrid of Norway
William and Kate's son will also joined Prince Moulay Hassan of Morocco as one of the world's male heirs to a throne. Prince Moulay Hassan, who celebrated his 10th birthday in May, is the son of King Mohammed I and Princess Lalla Salma of Morocco.
In giving birth to a boy Prince George will be outnumbered among the future queens in Europe as Norway, Belgium, Sweden, Spain and the Netherlands all have female heirs.
Princess Amalia of the Netherlands, Princess Leonor of Spain, Princess Ingrid of Norway and Princess Elisabeth of Belgium all share the same royal destiny; as does Princess Estelle of Sweden, one, who is the youngest of the group and will be closest in age to William and Kate's son.