In the royal family, there is a precedent of the second son succeeding the throne. I'm sure there are lots of examples of this being so* but two men who immediately come to mind are King George V and his son, King George VI. Neither of these men expected, or likely anticipated that they would become kings.
The future King George V, Prince George, Duke of York, became heir to the throne after his older brother, Prince Albert Victor, Duke of Clarence and Avondale died unexpectedly at the age of 28. Prince George had been pursuing a military career, which was regarded as the most suitable occupation for the second son. Prince Albert Victor, at the time of his death third-in-line for the throne, was to be married a month later to Princess May of Teck, but he died on January 14th, 1892. Prince George then became heir, and in time 'inherited' his brother's fiance, the future Queen Mary.
Unlike his future son, Prince Albert, King George V had plenty of time to adapt to his new role before he himself became king in 1910. His own father, King Edward VII, despite being the longest serving heir to the throne - 59 years, had little training himself, as his mother Queen Victoria didn't allow him access to her papers. Despite this, King Edward VII went on to become a successful monarch who gave his name to an era. During his reign, King Edward VII made certain that his son was well trained when the time came for him to succeed.
King George V had five sons and one daughter, Edward - Prince of Wales, Albert - Duke of York, Mary - Princess Royal, George - Duke of Kent, Henry - Duke of Gloucester, and John - who died as a child. Edward had been destined to be king from birth and he eventually would succeed the throne in 1936 upon the death of his father. However, Edward decided to abdicate to marry Wallis Simpson and his brother, Albert - who was seen as a rather unlikely candidate for the throne, became King George VI in the same year (incidently 1936 is known as the year of three kings). King George VI wasn't nearly as well trained as his father had been but he eventually became a good king. As the father of the present Queen, he ensured that she had the best possible training for her future role.
While it's hard to ignore precedent, I doubt that Prince Harry would have the same type of training. Is he qualified? Yes - from the moment of his birth. There really isn't anything that defines what criteria makes a good monarch. You'd be hard pressed to find a career counsellor who could tell you. Should something unfortunate happen to William, hopefully Harry will have plenty of time to adapt to his new role. He could have no better instructor than his grandmother.
© Marilyn Braun 2007
* if anyone knows of other examples, feel free to comment.