Experts say that the name Prince William has a deep meaning behind it.
The first child of Prince Charles and Princess Diana, and second in line to the throne, William was almost named Arthur by his father.
It was Diana, who instead wanted a stronger name for her firstborn.
Royal biographer Robert Lacey told People: "Princess Diana of Wales proposed a more robust name—William, as in 'William the Conqueror', victor of the famous Battle of Hastings in 1066."
However, experts say that there was another reason for the future king to be named William.
The father of three is named after a deceased member of the royal family who was famous for his adventurous lifestyle.
Prince William Henry Andrew Frederick was born in Barnet in December 1941 to Prince Henry, Duke of Gloucester and Alice, Duchess of Gloucester.
He was the grandson of the late King George V and Queen Mary and died tragically young in a plane crash.