William is doing everything he could so that he would be prepared when his turn comes to be the King of England, even though he is the second in the line of succession. Furthermore, his wife is also preparing for the future role as a queen.
When will this happen?
William and Kate have been together since 2001 and their relationship was crowned with the marriage in 2011. From the moment they married, they were aware of the roles they have in the royal family and England. However, William is second in the line of succession, and he would need to wait for the Queen to die, then Charles becomes the King and William would be the King after his death. If we take into account the longevity of the members of the royal family, it can be decades until William becomes a king. Regardless of this, William is doing everything he could in order to be prepared for this role and Kate is following him in this.
When Elizabeth II became the Queen of England, her husband, i.e. Prince Philip, did not become a king, he remained a prince. The reason for this is the fact that according to rules, if a female is a monarch, her husband can never become a king.
It should be mentioned that the situation with Kate may be somewhat different than with Philip. The reason for this is the fact that in England, a wife of a king can become a queen. So, the official Kate’s title when her husband becomes a king would be the Queen Consort. This term “consort” is actually used to point out that she would not be a ruler per se but she would be the queen, nonetheless. She would be appointed as a queen during the ceremony in which William would be crowned as a king.
However, there is not a rule that a wife of a king is automatically becoming a queen. This decision is in essence the decision of the royal family and the family may bring the other decision, i.e. the title of the King’s wife may not change after the coronation of her husband. When it comes to Camilla Parker Bowles, the chances that the royal family would decide for her to be the Queen Consort are pretty small, or non-existent. The reason for this is the fact that the public, and also the majority of the royal family, actually does not like Camilla, and this is the reason why she would most probably remain the Duchess of Cornwall when Charles becomes a king one day. All this would be known only when the Queen steps down from the throne.